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EARTH 

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LIBRARY 


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GIFT  OF 
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KARTH 
ENCES 


THE  PRIMARY  FACTORS 


ORGANIC  EVOLUTION 


E.  D.  COPE,  PH.  D. 

MEMBER  OF  THE  U.  S.  NATIONAL  ACADEMY  OF  SCIENCES;    PROFESSOR 

OF  ZOOLOGY  AND  COMPARATIVE  ANATOMY  IN  THE 

UNIVERSITY  OF  PENNSYLVANIA 


CHICAGO 

THE  OPEN  COURT  PUBLISHING  COMPANY 

(LONDON:  17  JOHNSON'S  COURT,  FLEET  ST.,  E.  C.) 

1904 


EARTH 

S91ENCE3 

LIBRARY 


COPYRIGHT  BY 

THE  OPEN  COURT  PUBLISHING  Co. 

CHICAGO,  ILL.,   1896. 


-Osx^JO 

-»e  ^w, 


R.    R.   DONNELLEY    &    SONS   CO.,  CHICAGO. 


PREFACE. 


THE  present  book  is  an  attempt  to  select  from  the  mass  of 
facts  accumulated  by  biologists,  those  which,  in  the  author's 
opinion,  throw  a  clear  light  on  the  problem  of  organic  evolution, 
and  especially  that  of  the  animal  kingdom.  As  the  actual  lines  of 
descent  can  be  finally  demonstrated  chiefly  from  paleontologic  re- 
search, I  have  drawn  a  large  part  of  my  evidence  from  this  source. 
Of  course,  the  restriction  imposed  by  limited  space  has  compelled 
the  omission  of  a  great  many  facts  which  have  an  important  bear- 
ing on  the  problem.  I  have  preferred  the  paleontologic  evidence 
for  another  reason.  Darwin  and  the  writers  of  his  immediate 
school  have  drawn  most  of  their  evidence  from  facts  which  are 
embraced  in  the  science  of  cecology.  Weismann  and  writers  of 
his  type  draw  most  of  their  evidence  from  the  facts  of  embryology. 
The  mass  of  facts  recently  brought  to  light  in  the  field  of  paleon- 
tology, especially  in  the  United  States,  remained  to  be  presented, 
and  the  evidence  they  contain  interwoven  with  that  derived  from 
the  sources  mentioned. 

Many  of  the  zoologists  of  this  country,  in  common  with  many 
of  those  of  other  nations,  have  found  reason  for  believing  that  the 
factors  of  evolution  which  were  first  clearly  formulated  by  La- 
marck, are  really  such.  This  view  is  taken  in  the  following  pages, 
and  the  book  may  be  regarded  as  containing  a  plea  on  their  behalf. 
In  other  words,  the  argument  is  constructive  and  not  destructive. 
The  attempt  is  made  to  show  what  we  know,  rather  than  what  we 
do  not  know.  This  is  proper  at  this  time,  since,  in  my  opinion,  a 
certain  amount  of  evidence  has  accumulated  to  demonstrate  the 
doctrine  here  defended,  and  which  I  have  defended  as  a  working 
hypothesis  for  twenty-five  years. 

In  the  following  pages  I  have  cited  many  authors  who  have 
contributed  to  the  result,  but  it  has  been  impossible  to  cite  all  who 


M  2716 


vi     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION-. 

have  written  on  one  part  or  another  of  the  subject.  If  some  very 
meritorious  essays  have  not  been  cited,  it  has  been  generally  be- 
cause I  have  confined  myself  to  those  in  which  facts  or  doctrines 
were  first  presented,  and  have  not  had  so  much  occasion  to  refer  to 
those  of  later  date. 

Mr.  Romanes,  in  his  posthumous  book,  Volume  II.  of  his  Dar- 
win, and  After  Darwin  on  Post- Darwinian  Questions,  expresses 
the  following  opinion  of  the  position  which  has  been  taken  by  the 
Neo-Lamarckians  of  this  country.  He  says  that  they  do  not  dis- 
tinguish between  the  "statement  of  facts  in  terms  of  a  proposition, 
and  an  explanation  of  them  in  terms  of  causality."  Had  Mr.  Ro- 
manes been  acquainted  with  the  literature  of  the  subject  published 
in  America  and  elsewhere  during  the  last  three  years,  he  would 
have  had  reason  to  change  this  view  of  the  case.  I  think  he  would 
have  found  in  it  demonstration  "in  terms  of  causality." 

At  the  outset  it  must  be  stated  that  a  knowledge  of  the  history 
of  organic  evolution  rests  primarily  on  the  science  of  morphology, 
and  secondarily  on  the  kinematics  of  the  growth  of  organic  struc- 
tures. The  phenomenon  to  be  explained  is  the  genealogical  suc- 
cession, or  phylogeny  of  organisms  ;  and  the  access  to  this  subject 
is  through  the  sciences  of  paleontology  and  embryology.  The  phe- 
nomena of  the  functioning  of  the  organism,  or  physiology,  are  only 
incidentally  referred  to,  as  not  the  real  object  of  inquiry.  Since 
organic  species  are  much  more  numerous  than  the  tissues  of  which 
they  are  composed,  organogenesis  must  claim  attention  more  largely 
than  histogenesis.  It  is  true  that  histogenesis  is  fundamental,  but 
it  is  a  science  as  yet  in  its  early  infancy,  and  little  space  can  be 
given  to  it.  The  exact  how  of  organic  evolution  will  never  be 
finally  solved,  however,  until  our  knowledge  of  histogenesis  is  com- 
plete. 

The  research  depicted  in  the  following  pages  has  proceeded  on 
the  assumption  that  every  variation  in  the  characteristics  of  organic 
beings,  however  slight,  has  a  direct  efficient  cause.  This  assump- 
tion is  sustained  by  all  rational  and  philosophical  considerations. 
Any  theory  of  evolution  which  omits  the  explanation  of  the  causes 
of  variations  is  faulty  at  the  basis.  Hence  the  theory  of  selection 
cannot  answer  the  question  which  we  seek  to  solve,  although  it 
embraces  an  important  factor  in  the  production  of  the  general  re- 
sult of  evolution. 

In  the  search  for  the  factors  of  evolution,  we  must  have  first  a 
knowledge  of  the  course  of  evolution.  This  can  only  be  obtained 


PREFACE.  vii 

in  a  final  and  positive  form  by  investigation  of  the  succession  of 
life.  The  record  of  this  succession  is  contained  in  the  sedimentary 
deposits  of  the  earth's  crust,  and  is  necessarily  imperfect.  Advance 
in  knowledge  in  this  direction  has,  however,  been  very  great  of  re- 
cent years,  so  that  some  parts  of  the  genealogical  tree  are  tolerably 
or  quite  complete.  We  hope  reasonably  for  continued  progress  in 
this  direction,  and  if  the  future  is  to  be  judged  of  by  the  past,  the 
number  of  gaps  in  our  knowledge  will  be  greatly  lessened.  In  the 
absence  of  the  paleontologic  record,  we  necessarily  rely  on  the  em- 
bryologic,  which  contains  a  recapitulation  of  it.  The  imperfections 
of  the  embryonic  record  are,  however,  great,  and  this  record  differs 
from  the  paleontologic  in  that  no  future  discovery  in  embryology 
can  correct  its  irregularities.  On  the  contrary  every  paleontologic 
discovery  is  an  addition  to  positive  genealogy,  if  the  present  work 
has  any  merit,  it  is  derived  from  the  fact  that  the  basis  of  the  argu- 
ment is  the  paleontologic  record. 

E.  D.  COPE. 
PHILADELPHIA,  November  i,  1895. 


CONTENTS. 


PAGE 

PREFACE     v 

TABLE  OF  CONTENTS ix 

LIST  OF  ILLUSTRATIONS xiii 

INTRODUCTION  .  i 


PART  I.     THE  NATURE  OF  VARIATION. 

PRELIMINARY 19 

CHAPTER  I.     VARIATION. 

Preliminary 21 

1.  Variations  of  Specific  Characters 25 

a.  Variations  in  Cicindela 25 

b.  Variations  in  Osceola  doliata 29 

c.  Color- Variations  in  Cnemidophorus 41 

d.  Variations  in  North  American  Birds  and  Mam- 

mals in  Relation  to  Locality 45 

2.  Variation  of  Structural  Characters 58 

3.  Successional  Relation 62 

CHAPTER  II.     PHYLOGENY. 

1.  General  Phylogeny 74 

2.  Phylogeny  of  the  Vertebrata 83 

a.  Phylogeny  of  the  Classes 83 

b.  The  Line  of  the  Pisces 99 

c.  The  Line  of  the  Batrachia    ....'...  108 

d.  The  Line  of  the  Reptilia 113 

e.  The  Line  of  the  Aves 123 

/.   The  Line  of  the  Mammalia 126 

g.   Review  of  the  Phylogeny  of  the  Mammalia          .  138 


x        PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

PAGE 

h.   Phylogeny  of  the  Horse 146 

i.  The  Phylogeny  of  Man 150 

3.  The  Law  of  the  Unspecialized 172 

CHAPTER  III.     PARALLELISM. 

Preliminary 175 

1.  Parallelism  in  the  Brachiopoda 176 

2.  Parallelism  in  the  Cephalopoda 182 

3.  Parallelism  in  the  Vertebrata 192 

4.  Inexact  Parallelism  or  Caenogeny 200 

5.  Objections  to  the  Doctrine  of  Parallelism 205 

CHAPTER  IV.     CATAGENESIS.  .  211 


PART  II.     THE  CAUSES  OF  VARIATION. 

PRELIMINARY 225 

CHAPTER  V.     PHYSIOGENESIS. 

Preliminary 227 

a.  Relation  of  Size  of  Mollusca  to  Environment .     .  229 

b.  The  Conversion  of  Artemia  into  Branchinecta      .  229 

c.  Production  of  Colors  in  Lepidopterous  Pupae  .     .  230 

d.  Effect  of  Light  on  the  Colors  of  Flatfishes  .     .     .238 

e.  Effect  of  Feeding  on  Color  in  Birds 238 

f.  Blindness  in  Cave  Animals 241 

CHAPTER  VI.     KINETOGENESIS. 

Preliminary 246 

1.  Kinetogenesis  of  Muscular  Structure 249 

2.  Kinetogenesis  in  Mollusca 255 

a.  Origin  of  the  Plaits  in  the  Columella  of  the  Gas- 

teropoda     255 

b.  Mechanical  Origin  of  Characters  in  the  Lamelli- 

branchiata 261 

c.  Mechanical    Origin   of   the    Impressed    Zone   in 

Cephalopoda 268 

3.  Kinetogenesis  in  Vermes  and  Arthropoda 268 

4.  Kinetogenesis  in  Vertebrata 275 

i.  Kinetogenesis  of  Osseous  Tissue 275 

a.   Abnormal  Articulations 275 


CONTENTS. 


b.  Normal  Articulations 283 

c.  The  Physiology  of  Bone  Moulding 285 

ii.   Moulding  of  the  Articulations 287 

a.  The  Limb  Articulations 287 

b.  The  Forms  of  Vertebral  Centra 302 

iii.  Increase  of  Size  Through  Use 304 

a.  The  Proportions  of  the  Limbs  and  their  Segments  305 

b.  The  Number  of  the  Digits 309 

c.  The  Horns 314 

iv.   Mechanical  Origin  of  Dental  Types 318 

Preliminary 318 

a.  The  Origin  of  Canine  Teeth .  327 

b.  The  Development  of  the  Incisors 328 

c.  The  Development  of  Molars 331 

d.  Origin  of  the  Carnivorous  Dentition        ....  332 

e.  Origin  of  the  Dental  Type  of  the  Glires ....   345 
v.  Disuse  in  Mammalia 352 

a.  Natatory  Limbs 352 

b.  Abortion  of  Phalanges  in  Ungulata 353 

c.  Atrophy  of  Ulna  and  Fibula 355 

d.  Atrophy  of  Incisor  Teeth 356 

vi.   Homoplassy  in  Mammalia 357 

vii.  Origin  of  the  Divisions  of  Vertebrata 362 

5.  Objections  to  Kinetogenesis 375 

CHAPTER  VII.     NATURAL  SELECTION  ..." 385 

PART  III.     THE  INHERITANCE  OF  VARIATION. 

PRELIMINARY 397 

CHAPTER  VIII.     HEREDITY. 

1.  The  Question  Stated 398 

2.  Evidence  from  Embryology 401 

a.  Vertebrata 401 

b.  Arthropoda 404 

3.  Evidence  from  Paleontology 405 

a.  The  Impressed  Zone  of  the  Nautiloids   ....  405 

4.  Evidence  from  Breeding 422 

a.  Of  Characters  Due  to  Nutrition 423 

b.  Of  Characters  Due  to  Exercise  of  Function     .     .  426 

c.  Of  Characters  Due  to  Disease 430 


xii     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


d.  Of  Characters  Due  to  Mutilation  and  Injuries      .  431 

e.  Of  Characters  Due  to  Regional  Influences  .     .     .435 

5.  The  Conditions  of  Inheritance 438 

6.  Objections  to  the  Doctrine  of  Inheritance  of  Acquired 

Characters 458 

CHAPTER  IX.     THE  ENERGY  OF  EVOLUTION. 

Preliminary 473 

1.  Anagenesis > 475 

2.  Bathmogenesis 484 

CHAPTER  X.     THE  FUNCTION  OF  CONSCIOUSNESS. 

1.  Consciousness  and  Automatism 495 

2.  The  Effects  of  Consciousness 509 

CHAPTER  XI.     THE  OPINIONS  OF  NEO-LAMARCKIANS  .  .   518 


LIST  OF  ILLUSTRATIONS. 


Fig.     i.  Horn  on  Cicindela 27 

2.  Osceola  doliata  triangula 32 

3.  Osceola  doliata  clerica 32 

4.  Osceola  doliata  collaris 34 

5.  Osceola  doliata  temporalis 34 

6-7.    Osceola  doliata  doliata 36 

8.  Osceola  doliata  syspila 38 

9.  Osceola  doliata  parallela 38 

10.  Osceola  doliata  annulata 40 

11.  Osceola  doliata  coccinea 40 

12.  Cnemidophorus  tessellatus 42 

13.  Cnemidophorus  gularis 43 

14.  Lacerta  muralis 44 

15.  Shoulder-girdle  of  Phyllomedusa  bicolor 64 

16.  Do.  of  Rana  temporaria,  tadpole  with  budding  limbs.  64 

17.  Do.,  adult 64 

18.  Bufonidae 66 

19.  Scaphiopidae  and  Pelobatidae 66 

20.  Hylidas 67 

21.  Cystignathidae 67 

22.  Ranidae 67 

23.  Feet  of   Unia  scoparia  Cope,  and  Ptenopus  garrulus 

Smith 72 

24.  Eusthenopterum  foordii  Whiteaves 90 

25.  Paired  fins  of  Cladoselache  Dean 92 

26.  Extremities  of  skeletons  of  caudal  fins  of  fishes     .     .  96 

27.  Cricotus  crassidiscus  Cope,  head  and  belly    .     .     .     .  in 

28.  Cricotus  crassidiscus  Cope,  vertebral  column  and  pelvis  112 


xiv     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

PAGE 

Fig.  29.  Crania  of  Stegocephalia  and  Cotylosauria    .     .     .     .117 

30.  Diagrams  of  crania  of  Reptilia 118 

31.  Do 119 

32.  Archceopteryx  lithographica  Wagn 125 

33.  Ungulata,  anterior  feet 129 

34.  Ungulata,  posterior  feet 130 

35.  Ungulata,  anterior  and  posterior  feet 131 

36.  Phenacodus  vortmanii  Cope 134 

37.  Fore  and  hind  limbs  of  Phenacodus  primavi.s  and 

Homo  sapiens 137 

38.  Skull  of  Anaptomorphus  homunculus  Cope.     Lower 

jaw  of  Anaptomorphus  cemulus  Cope 151 

39.  Tomitherium  rostratum  Cope,  mandible 156 

40.  Tomitherium  rostratum  Cope,  fore  arm 157 

41.  Tomitherium  rostratum  Cope,  ilium  and  femur      .      .158 

42.  Megaladapis  madagascariensis  Forsyth  Major    .      .      .    160 

43.  Skull  of  the  man  of  Spy 161 

44.  Outlines  of  calvaria  of  the  Neanderthal  man,  of  the 

Spy  men.     .     .  . 162 

45.  Vertical  sections  of  symphysis  mandibuli  of  gorilla  ; 

of  orang  ;  of  chimpanzee  ;  of  Spy  men     ....   164 

46.  Sections  of  symphysis  mandibuli  of  modern  Liegois 

and  of  an  ancient  Parisian 166 

47.  Molar  teeth  of  man ....  167 

48.  Parallelism  in  Brachiopoda  ....  .     .     .     .  181 

49.  Circulatory  systems 194 

50.  Succession  of  horns  of  Cervits  elaphus  L 197 

51.  Shoulder-girdles  of  Anura 198 

52.  Lernaa  branchialis 212 

53.  Entoconcha  mirabilis  Mull 214 

54.  Mycetozoa 220 

55-    Typhlogobius  californiensis  Steind 245 

56.  Fusus parilis  Con.,  displaying  non-plicate  columella.   257 

57.  Mitra  lineolata  Heilprin,  showing  the  plications  of  the 

columella     .     - 259 

58.  Siphocyprcea  problematica   Heilprin,    showing    plica- 

tions of  lips 260 

59.  Ostrea  edulis,  embryo 262 

60.  Mya  arenaria 263 

61.  Modiola  plicatula 264 


LIST  OF  ILLUSTRATIONS.  xv 


Fig.  62.    Ostrea  virginiana 264 

63.  Diagrammatic  representation  of  the  segments  of  the 

leech 270 

64.  Diagrammatic  representation  of  the  rings  of  a  primi- 

tive crustacean 271 

65.  Diagrams  of  hand  of  Crangon  and  of  Astacus  .     .     .  274 

66.  Elbows  of  man  and  horse 280 

67.  Elbow  of  horse •     .     .  281 

68.  Periptychus  rhabdodon  Cope,  showing  foot    ....  288 

69.  Hind  foot  of  Poebrotherium  labiatum  Cope  ....  290 

70.  Hind  foot  of  three-toed  horse 290 

71.  United  first  bones  of  two  middle  toes  of  deer-antelope  291 

72.  Wrist-joints  at  distal  extremity  of  fore  arm       .     .     .  292 

73.  Elbow-joint  of  Crocuta  maculata  L 294 

74.  Elbow-joint  of  chimpanzee 295 

75.  Elbow -joint  of  Cervus  elaphus 296 

76.  Cervus  canadensis  in  motion 297 

77.  Cervus  elaphus 298 

78.  Diagram  of  carpus  of  a  Taxeopod,  of  a  diplarthrous 

ungulate 299 

79.  Raccoon  pacing 299 

80.  Rhinocerus  unicornis  carpus 300 

81.  Equus  caballus  fore  foot 300 

82.  Gazella  dorcas 301 

83.  Pes  of  Merychochcerus  montanus  and  Bos  taurus    .     .  307 

84.  Anterior  feet  of  primitive  Ungulata 308 

85.  Righ t  posterior  foot  of  Prothippus  and  Poebrotherium  310 

86.  Manus  of  Artiodactyla 312 

87.  Burrs  on  antlers  of  Cosoryx  necatus  Leidy    ....  316 

88.  Diagram  of  excursion  of  lower  jaw  in  mastication      .  320 

89.  Cervus,  molars 321 

90.  Cusps  of  superior  premolars  and  molars 322 

91.  Two  true  molars  of  both  jaws  of  a  ruminant     .     .     .  323 

92.  Sections  of  superior  molar  teeth 323 

93.  Chirox plicatus  Cope,  palate  and  molar  teeth    .     .     .   324 

94.  Meniscoessus  conquistus  Cope,  last  two  superior  mo- 

lars      325 

95.  Lemur  collaris,  dentition 326 

96.  Esthonyx  burmeisterii  Cope,  dentition 328 


xvi     PRIMAR  Y  FA CTORS  OF  ORGANIC  E  VOL  UT1ON. 

PAGE 

Fig.  97.   Psittacotherium   multifragum  Cope,   mandibular  ra- 

mus 329 

98.  Diagrammatic  representations  of  horizontal  sections 

of  tricuspidate  molars  of  both  jaws  in  mutual  rela- 
tion      333 

99.  Deltatheriumfundaminis  Cope,  fragmentary  skull      .   336 

100.  Centetes  ecaudatus,  skull  and  molars 337 

101.  Inferior  molar  crowns  representing  transition  from 

the  simple  to  the  quadritubercular 338 

102.  Stypholophus    whitice    Cope ;    apposition  of  inferior 

and  superior  molars 339 

103.  Cynodictis  geismarianus  Cope  ;  skull 341 

104.  Aelurodon  sizvus  Leidy;    coadaptation  of  crowns  of 

superior  and  inferior  molars  in  mastication    .     .     .  342 

105.  Smilodon  neogczus  Lund  ;  skull 344 

106.  Sections  of  crowns  of  molars  of  Ungulata     ....  345 

107.  Castorotdes  ohioensis  Foster  ;  skull 347 

108.  Castoro'ides  ohioensis  Foster  ;  skull  from  below      .      .   350 

109.  Ischyromys  typus  Leidy  ;  cranium  and  mandible    .     .  351 

i  jo.  Balcena  mysticetus  ;  fore  limb 353 

in.  Feet  of  Amblypoda 354 

112.  Feet  of  Proterotheriidae 358 

113.  Dorsal  vertebrae  of  merospondylous  fishes    ....  370 

114.  Vertebral  column  of  Eryops  megacephalus  Cope     .     .  371 
1 140  Sleeve  of  coat 371 

115.  Metatoceras  cavatiformis  Hyatt 406 

116.  Do 407 

117.  Temnochilus  crassus 407 

118.  Metacoceras  dubium  Hyatt 408 

119.  Hyatt  on  Cephalopoda 410 

120.  Diagram  explanatory  of  Diplogenesis 441 


INTRODUCTION. 


THE  doctrine  of  evolution  may  be  defined  as  the 
teaching  which  holds  that  creation  has  been  and 
is  accomplished  by  the  agency  of  the  energies  which 
are  intrinsic  in  the  evolving  matter,  and  without  the 
interference  of  agencies  which  are  external  to  it.  It 
holds  this  to  be  true  of  the  combinations  and  forms  of 
inorganic  nature,  and  of  those  of  organic  nature  as 
well.  Whether  the  intrinsic  energies  which  accom- 
plish evolution  be  forms  of  radiant  or  other  energy 
only,  acting  inversely  as  the  square  of  the  distance, 
and  without  consciousness,  or  whether  they  be  ener- 
gies whose  direction  is  affected  by  the  presence  of  con 
sciousness,  the  energy  is  a  property  of  the  physical 
basis  of  tridimensional  matter,  and  is  not  outside  of  it, 
according  to  the  doctrine  we  are  about  to  consider. 

As  a  view  of  nature  from  an  especial  standpoint, 
evolution  takes  its  place  as  a  distinct  science.  The 
science  of  evolution  is  the  science  of  creation,  and  is 
as  such  to  be  distinguished  broadly  from  the  sciences 
which  consider  the  other  operations  of  nature,  or  the 
functioning  of  nature,  which  are  not  processes  of  crea- 
tion, but  processes  of  destruction.  This  contrast  is 
especially  obvious  in  organic  evolution,  where  the  two 
processes  go  on  side  by  side,  and  are  often  closely  in- 


2       PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION, 

termingled,  as  for  instance  in  muscular  action,  where 
both  destruction  of  proteids  and  growth  of  muscular 
tissue  result  from  the  same  acts,  or  use.  Physiology, 
or  the  science  of  functions,  concerns  itself  chiefly  with 
destruction,  and  hence  physiologists  are  especially 
prone  to  be  insensible  to  the  phenomena  and  laws  of 
progressive  evolution.  The  building  of  the  embryo, 
remains  a  sealed  book  to  the  physiologist  unless  he 
take  into  account  the  allied  biological  science  of  evo- 
lution, as  resting  on  the  facts  of  botany,  zoology,  and 
paleontology.  In  his  reflections  on  the  relations  of 
mind  to  matter  he  is  likely  to  see  only  the  destructive 
functioning  of  tissue,  and  not  the  history  of  the  build- 
ing of  the  same  during  the  ages  of  geological  time. 

J.  B.  P.  A.  Lamarck1  thus  contrasts  the  theories 
of  direct  creation,  and  creation  by  evolution.  The 
former  asserts  :  "That  nature  or  its  author  in  creating 
animals  has  foreseen  all  possible  kinds  of  circumstances 
in  which  they  may  have  to  live,  and  has  given  to  each 
species  a  permanent  organization  as  well  as  a  prede- 
termined form,  invariable  in  its  parts  ;  that  it  forces 
each  species  to  live  in  the  place  and  the  climate  where 
one  finds  them,  and  to  preserve  there  the  habits  which 
it  has."  He  then  states  his  own,  or  the  evolutionary, 
opinion  to  be:  "That  nature  in  producing  succes- 
sively all  species  of  animals,  commencing  with  the 
most  imperfect  or  simple,  and  terminating  its  work 
with  the  most  perfect,  has  gradually  complicated  their 
organization  ;  and  these  animals  spreading  themselves 
gradually  into  all  habitable  regions  of  the  globe,— 
each  species  has  been  subjected  to  the  influence  of  the 
circumstances  in  which  it  is  ;  and  these  have  produced 
the  habits  which  we  observe,  and  the  modifications  of 

\Philosophie  Zoologique,  Paris,  1809,  Vol.  I.,  Chap.  VII. 


INTRODUCTION.  3 

its  parts."  On  an  earlier  page  of  the  same  chapter, 
Lamarck  thus  formulates  the  laws  of  organic  evolu- 
tion, to  which  his  name  has  been  attached. 

First  law.  "  In  every  animal  which  has  not  passed 
the  time  of  its  development,  the  frequent  and  sustained 
employment  of  an  organ  gradually  strengthens  it,  de- 
velops and  enlarges  it,  and  gives  it  power  proportional 
to  the  duration  of  its  use  ;  while  the  constant  disuse 
of  a  like  organ  weakens  it,  insensibly  deteriorates  it, 
progressively  reduces  its  functions,  and  finally  causes 
it  to  disappear." 

Second  law.  "All  that  nature  acquires  or  loses  in 
individuals  by  the  influence  of  circumstances  to  which 
the  race  has  been  exposed  for  a  long  time,  and  in  con- 
sequence of  the  influence  of  the  predominate  employ- 
ment of  such  an  organ,  or  of  the  influence  of  disuse  of 
such  part,  she  preserves  by  generation,  in  new  indi- 
viduals which  spring  from  it,  providing  the  acquired 
changes  be  common  to  both  sexes,  or  to  those  which 
have  produced  new  individuals. " 

We  have  here  a  theory  of  the  origin  of  characters ; 
viz.,  of  the  increased  development  or  loss  of  parts  as 
a  result  of  use  or  disuse.  We  have  also  the  theory 
that  the  peculiarities  thus  acquired  are  transmitted  to 
the  succeeding  generation  by  inheritance. 

The  next  formal  statement  of  the  efficient  cause  of 
organic  evolution  was  presented  by  Messrs.  Charles 
Darwin  and  Alfred  R.  Wallace  in  I859.1  The  cause 
assigned  is  natural  selection,  and  Mr.  Darwin  thus 
states  what  is  meant  by  this  expression  in  his  work 
The  Origin  of  Species.'1  "  If  under  changing  conditions 
of  life  organic  beings  present  individual  differences 

1  Proceedings  of  the  Linnean  Society  of  London. 

2  Ed.  1872,  p.  102. 


4      PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

in  almost  any  part  of  their  structure,  and  this  cannot 
be  disputed  ;  if  there  be,  owing  to  their  geometrical 
rate  of  increase,  a  severe  struggle  for  life  at  some  age, 
season,  or  year,  and  this  certainly  cannot  be  disputed ; 
then  considering  the  infinite  complexity  of  the  rela- 
tions of  all  organic  beings  to  each  other  and  to  their 
conditions  of  life,  causing  an  infinite  diversity  of  struc- 
ture, constitution,  and  habits,  to  be  advantageous  to 
them,  it  would  be  a  most  extraordinary  fact  if  no  varia- 
tions had  ever  occurred  useful  to  each  being's  own  wel- 
fare, in  the  same  manner  as  so  many  variations  have 
occurred  useful  to  man.  But  if  variations  useful  to 
any  organic  being  ever  do  occur,  assuredly  individuals 
thus  characterized  will  have  the  best  chance  of  being 
preserved  in  the  struggle  for  life  ;  and  from  the  strong 
principle  of  inheritance,  these  will  tend  to  produce  off- 
spring similarly  characterized.  This  principle  of  pre- 
servation, or  the  survival  of  the  fittest,  I  have  called 
natural  selection.  It  leads  to  the  improvement  of  each 
creature  in  relation  to  its  organic  and  inorganic  condi- 
tions of  life  ;  and  consequently  in  most  cases,  to  what 
must  be  regarded  as  an  advance  in  organization. 
Nevertheless,  low  and  simple  forms  will  long  endure 
if  well  fitted  for  their  simple  conditions  of  life." 

It  is  readily  perceived  that  this  statement  makes 
no  attempt  to  account  for  the  origin  of  variations,  but 
that  it  simply  formulates,  as  observed  by  Mr.  Darwin, 
the  doctrine  of  survival  of  such  variations  as  are  most 
useful  to  their  possessors.  This  fact  is  more  distinctly 
pointed  out  in  the  same  work  (p.  63)  where  the  author 
remarks:  "Several  writers  have  misapprehended  or 
objected  to  the  term  natural  selection.  Some  have 
even  imagined  that  natural  selection  induces  variabil- 
ity, whereas  it  implies  only  the  preservation  of  such 


INTRO  D  UC  TION.  5 

variations  as  arise  and  are  beneficial  to  the  being  under 
its  conditions  of  life.  No  one  objects  to  agriculturists 
speaking  of  the  potent  effects  of  man's  selection,  and 
in  this  case  the  individual  differences  given  by  nature, 
which  man  for  some  object  selects,  must  of  necessity 
first  occur."  It  is  evident  then  that  Mr.  Darwin  did 
not  attempt  to  account  for  the  origin  of  variations,  but 
that  the  service  rendered  by  him  and  by  Mr.  Wallace 
to  the  doctrine  of  evolution  consists  in  the  demonstra- 
tion of  the  reality  of  natural  selection.  Darwin  also 
assumes  in  the  statement  first  quoted  above,  the  in- 
heritance of  acquired  characters. 

In  1865  the  Principles  of  Biology  of  Herbert  Spen- 
cer appeared.  In  this  work  the  attempt  is  made  to 
set  forth  the  laws  of  organic  evolution,  in  a  way  which 
represents  an  advance  beyond  the  positions  of  his 
predecessors.  He  adopts  and  harmonizes  both  the 
Lamarckian  and  Darwinian  doctrines,  and  is  at  times 
more  specific  in  his  application  of  Lamarck's  doctrine 
of  the  stimulus  of  the  environment,  and  of  use,  than 
was  Lamarck  himself.  Very  often,  however,  Spencer 
contents  himself  with  generalities ;  or  takes  refuge  in 
the  "instability  of  the  homogeneous,"  as  an  efficient 
cause.  This  phrase,  however,  like  his  other  one,  "the 
unknowable,"  is  but  a  makeshift  of  temporary  ignor- 
ance, and  is  neglected  by  Spencer  himself,  when  he 
can  see  his  way  through  it.  He  approaches  the  cause 
of  the  varied  forms  of  leaves  of  plants  in  this  language  r1 
"And  it  will  also  be  remembered  that  these  equalities 
and  inequalities  of  development  correspond  with  the 
equalities  and  inequalities  in  the  incidence  of  forces." 
Language  of  similar  significant  but  rather  indefinite 
import  is  frequently  used  throughout  this  volume. 

1  The  Principles  of  Biology,  by  Herbert  Spencer,  Amer.  Ed.,  1873,  II.,  p.  143. 


6      PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

But  in  some  cases  Spencer  is  more  specific.  With 
reference  to  the  inequality  in  the  basal  lobes  of  the 
erect  leaves  of  Tilia  and  other  plants,  he  says:1  "A 
considerable  deviation  from  bilateral  symmetry  may 
be  seen  in  a  leaf  which  habitually  so  carries  itself  that 
the  half  on  the  one  side  of  the  midrib  is  more  shaded 
than  the  other  half.  The  drooping  branches  of  the 
lime  show  us  leaves  so  arranged  and  so  modified.  On 
examining  their  attitudes  and  their  relations  one  to 
another,  it  will  be  found  that  each  leaf  is  so  inclined 
that  the  half  of  it  next  the  shoot  grows  over  the  shoot 
and  gets  plenty  of  light ;  while  the  other  half  so  hangs 
down  that  it  comes  a  good  deal  into  the  shade  of  the 
preceding  leaf.  The  result  is  that  having  learned  which 
fall  into  these  positions,  the  species  profits  by  a  large 
development  of  the  exposed  halves  ;  and  by  survival 
of  the  fittest  acting  along  with  the  direct  effect  of  extra 
exposure,  this  modification  becomes  established."  In 
his  discussion  of  the  origin  of  the  characters  of  ani- 
mals, Spencer  is  also  sometimes  specific.  Respecting 
the  development  of  muscular  insertions  he  remarks  :2 
"Anatomists  easily  discriminate  between  the  bones  of 
a  strong  man  and  those  of  a  weak  man  by  the  greater 
development  of  those  ridges  and  crests  to  which  the 
muscles  are  attached  ;  and  naturalists  on  comparing 
the  remains  of  domesticated  animals  with  those  of 
wild  animals  of  the  same  species,  find  kindred  differ- 
ences. The  first  of  these  facts  shows  unmistakably 
the  immediate  effect  of  function  on  structure,  and,  by 
obvious  alliance  with  it,  the  second  may  be  held  to  do 
the  same,  both  implying  that  the  deposit  of  dense  sub- 
stance capable  of  great  resistance  habitually  takes 

I  Op.  cit.,  p.  143. 
ILoc.  cit.,  p.  200. 


INTR  OD  UC  TWN.  7 

place  at  points  where  the  tension  is  excessive."  Quite 
as  specific  is  his  ascription  of  the  forms  of  epithelial 
cells  to  definite  causes,  as  follows:1  " Just  the  equal- 
ities and  inequalities  of  dimensions  among  aggregated 
cells,  are  here  caused  by  the  equalities  and  inequalities 
among  their  mutual  pressures  in  different  directions  ; 
so  though  less  manifestly,  the  equalities  and  inequali- 
ties of  dimensions  among  other  aggregated  cells,  are 
caused  by  the  equalities  and  inequalities  of  the  osmatic, 
chemical,  thermal,  and  other  forces  besides  the  me- 
chanical, to  which  their  different  positions  subject 
them." 

In  spite  of  this  not  infrequent  definiteness,  Mr. 
Spencer  occasionally  falls  into  the  error  of  ascribing 
the  origin  of  structures  to  natural  selection,  as  in  the 
case  of  the  forms  of  flowers,2  and  the  armor-plates  of 
paleozoic  fishes.3  Spencer  assumes  the  inheritance  of 
acquired  characters  throughout. 

In  1866  Haeckel's  Schopfungsgeschichte  appeared. 
In  this  work  the  author  presents  a  mass  of  evidence 
which  sustains  the  doctrine  of  evolution,  and  he  com- 
bines the  views  of  Lamarck  and  Darwin  into  a  general 
system.  He  says:4  "We  should,  on  account  of  the 
grand  proofs  just  enumerated,  have  to  adopt  Lamarck's 
theory  of  descent  for  the  explanation  of  biological  phe- 
nomena, even  if  we  did  not  possess  Darwin's  theory  of 
selection.  The  one  is  so  completely  and  directly  proved 
by  the  other,  and  established  by  mechanical  causes, 
that  there  remains  nothing  to  be  desired.  The  laws 
of  inheritance  and  adaptation  are  universally  acknowl- 

1  Op.  cit.,  p.  260. 

2  Op.  cit.,  p.  153. 
3<9/.  cit.,  p.  288. 

*The  History  of  Creation,  Amer.  Edition,  II.,  p.  355. 


8      PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

edged  physiological  facts,  the  former  traceable  to  prop- 
agation, the  latter  to  the  nutrition  of  organisms." 
Apart  from  the  statement  that  adaptation  is  traceable 
"to  the  nutrition  of  organisms,"  we  find  nothing  in 
Haeckel's  earlier  writings  which  attempts  the  ex- 
planation of  the  origin  of  variations,  beyond  the  gen- 
eral position  assumed  by  Lamarck.  The  distinctive 
merit  of  Haeckel  is  his  formulation  of  phylogeny.  Much 
of  this  was  speculative  at  the  time  he  wrote,  but  so  far 
as  the  Vertebrata  are  concerned,  it  has  been  largely 
confirmed  by  subsequent  discovery. 

Up  to  this  period,  the  form  in  which  the  doctrine 
of  evolution  had  been  presented,  was  general  in  its 
application ;  that  is,  without  exact  reference  to  the 
structural  definitions  of  natural  taxonomic  groups.  No 
attempt  was  made  to  show  the  modes  of  the  origin  of 
any  particular  class,  order,  or  genus,  and  only  in  the 
most  general  way  in  the  case  of  a  few  species,  by  Mr. 
Darwin.  Phylogeny  was  untried,  except  by  Haeckel; 
and  this  distinguished  author  did  not  attempt  to  ac- 
count specifically  for  the  origins  of  the  divisions  whose 
filiations  he  set  forth. 

In  the  year  in  which  Haeckel's  work  above  cited 
appeared,  Professor  Hyatt  of  Boston  and  myself  took 
the  first  step  towards  the  formulization  of  a  rational 
theory  of  the  origin  of  variation,  which  should  accord 
with  specific  examples  of  taxonomy.  Quite  indepen- 
dently, we  selected  the  simple  series  presented  by  the 
characters  of  genera  in  their  natural  relations,  Hyatt 
in  the  cephalopodous  Mollusca,  and  I  in  the  Batrachia 
Salientia.  It  is  probable  that  Hyatt's l  article  was  pub- 
lished shortly  before  mine.  He  says  of  the  genera  of 
Cephalopoda  :  "In  other  words,  there  is  an  increasing 

I  Memoirs  Boston  Society  Natural  History,  1866,  p.  193. 


INTR  OD  UC  TION.  9 

concentration  of  the  adult  characteristics  in  the  young 
of  higher  species  and  a  consequent  displacement  of 
other  embryonic  features  which  had  themselves  also 
previously  belonged  to  the  adult  period  of  still  lower 
forms."  My  own  language  is  i1  "That  the  presence, 
rudimental  condition,  or  absence  of  a  given  generic 
character  can  be  accounted  for  on  the  hypothesis  of  a 
greater  rapidity  of  development  in  the  individuals  of 
the  species  of  the  extreme  type,  such  stimulus  being 
more  and  more  vigorous  in  the  individuals  of  the  types 
as  we  advance  towards  the  same,  or  by  a  reversed  im- 
pulse2 of  development,  where  the  extreme  is  charac- 
terized by  absence  or  ' mutilation '  of  characters."  The 
phenomena  of  the  aggregation  of  characters  in  pro- 
gressive evolution,  and  the  loss  of  characters  in  retro- 
gressive evolution,  were  termed  by  me  acceleration  and 
retardation  in  an  essay  published  in  i86g.3  In  these 
papers  by  Professor  Hyatt  and  myself  is  found  the 
first  attempt  to  show  by  concrete  examples  of  natural 
taxonomy,  that  the  variations  that  result  in  evolution 
are  not  multifarious  or  promiscuous,  but  definite  and 
direct,  contrary  to  the  method  which  seeks  no  origin 
for  variations  other  than  natural  selection.  In  other 
words,  these  publications  constitute  the  first  essays  in 
systematic  evolution  that  appeared.  By  the  discovery 
of  the  paleontologic  succession  of  modifications  of  the 
articulations  of  the  vertebrate,  and  especially  mamma- 
lian skeleton,  I  first  furnished  an  actual  demonstration 
of  the  reality  of  the  Lamarckian  factor  of  use,  or  mo- 


1  Transactions  American  Philosophical  Society,   1866,   p.  398;  reprinted  in 
The  Origin  of  the  Fittest,  p.  92. 

2  The  expression  "  reversed  "  is  unfortunate,  diminished  being  the  proper 
word  to  convey  the  meaning  intended. 

3  The  Origin  of  Genera,  Philadelphia,  1869. 


io     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

tion,  as  friction,  impact,  and  strain,  as  an  efficient 
cause  of  evolution.1  This  demonstration  led  me  to  the 
necessary  inference  that  when  the  agency  directive  of 
motion  is  consciousness,  this  also  has  been  an  impor- 
tant factor  of  evolution,  in  demonstration  of  the  sup- 
position of  Erasmus  Darwin.2  Hyatt  has  demonstrated 
first  on  paleontologic  evidence,  the  inheritance  of  a 
mechanically  acquired  character.  Important  contribu- 
tions to  corresponding  histories  of  the  Mollusca  have 
been  made  by  Hyatt,3  Dall,4  Jackson,6  and  Beecher.5 
Many  other  contributions,  into  which  the  paleontologic 
evidence  does  not  enter,  have  also  been  made  by  vari- 
ous authors  in  Europe  and  America. 

The  authors  quoted  up  to  this  point  had  all  as 
sumed  that  the  progress  of  evolution  depends  on  the 
inheritance  by  the  offspring  of  new  characters  acquired 
by  the  parent,  and  had  believed  that  such  is  the  fact 
in  ordinary  experience.  In  1883,  Weismann,  in  an 
essay  on  heredity,  announced  the  opinion  that  charac- 
ters acquired  by  the  body  could  not  be  transmitted  to 
the  reproductive  cells,  and  could  not  therefore  be  in- 
herited. This  doctrine  rests  on  the  relation  of  the 
germ-cells  to  those  of  the  rest  of  the  body,  which  is 
expressed  in  the  following  language  of  his  predecessor 
Jaeger:  "Through  a  great  series  of  generations  the 

l"The  Origin  of  the  Hard  Parts  of  Mammalia,"  American  Journal  of 
Morphology,  1889,  p.  137. 

2  Origin  of  the  Fittest,  1887,  p.  357. 

3"Phylogeny  of  an  Acquired  Characteristic,"  Proc.  Amer.  Philosophical 
Society,  1893,  p.  349;  "The  Genesis  of  the  Arietidae,"  Memoirs  Mus.  Compar. 
Zodlogy,  Cambridge,  Mass.,  1889,  XVI.,  No.  3. 

4 Dall,  W.  H.,  "The  Hinge  of  Pelecypods  and  Its  Development,  Amer. 
Jour.  Sci.  Arts,  1889,  XXXVIII.,  p.  445. 

SJackson,  R.  T.,  "  Phylogeny  of  the  Pelecypoda,  the  Aviculidae,  and  Their 
Allies,"  Memoirs  Boston  Society  Natural  History,  1890,  IV.,  p.  277. 

6 American  Journal  Sci,  Arts,  1893. 


INTRODUCTION.  n 

germinal  protoplasm  retains  its  specific  properties, 
dividing  in  every  reproduction  into  an  ontogenetic  por- 
tion and  a  phylogenetic  portion,  which  is  reserved  to 
form  the  reproductive  material  of  the  mature  offspring. 
This  reservation  of  the  phylogenetic  material  I  de- 
scribed as  the  continuity  of  the  germ-protoplasm.  .  .  . 
Encapsuled  in  the  ontogenetic  material  the  phyloge- 
netic protoplasm  is  sheltered  from  external  influences, 
and  retains  its  specific  and  embryonic  characters."  In 
other  words,  the  reproductive  cells  are  removed  from 
the  influence  of  those  stimuli  which  affect  and  effect 
growth  in  the  cells  of  the  other  parts  of  the  body,  so 
that  no  character  acquired  by  the  rest  of  the  body  can 
be  inherited.  The  bearing  of  this  theory  on  evolution 
is  thus  stated  by  Weismann  : L  "The  origin  of  heredi- 
tary individual  variations  cannot  indeed  be  found  in 
the  higher  organisms,  the  metazoa  and  metaphyta,  but 
is  to  be  sought  for  in  the  lowest,  the  unicellular."  "The 
formation  of  new  species,  which  among  the  lower  pro- 
tozoa could  be  achieved  without  amphigony  (sexual 
union),  could  only  be  attained  by  means  of  this  process 
in  the  metazoa  and  metaphyta.  It  was  only  in  this 
way  that  hereditary  individual  differences  could  arise 
and  persist. "  In  other  words,  variation  in  organic 
beings  above  the  unicellular  forms,  has  been  and  is, 
introduced  only  by  sexual  reproduction. 

The  conclusions  of  Weismann  were  derived  prin- 
cipally from  embryologic  research,  and  his  disciples 
have  been  chiefly  recruited  from  embryologists.  These 
conclusions  have  been  supported  by  extensive  and  ex- 
haustive investigations,  which  have  added  greatly  to 
our  knowledge  of  the  subject.  In  order  to  account  for 

1  Essays,  p.  296.     For  a   complete  account  of  Weismann's  views,  see  The 
Germ-Plasm,  1893. 


12     PRIMAR  Y  FA CTORS  OF  ORGANIC  E  VOL UTION. 

the  appearance  of  characters  in  the  embryonic  succes- 
sion, through  influences  confined  to  the  germ-plasma, 
Weismann  invented  a  theory  which  requires  the  pres- 
ence of  distinct  molecular  aggregates  within  it,  which 
represent  the  potentialities  or  causes.  To  these  he  has 
given  the  names  of  ids,  idants,  determinants,  etc.  As 
Weismann's  contribution  to  evolution  has  been  con- 
fined to  the  department  of  heredity,  I  will  consider  it 
more  particularly  in  the  third  part  of  this  book,  which 
is  devoted  to  that  subject. 

Weismann  has,  however,  subsequently  modified 
his  views  to  a  considerable  extent.  He  has  always 
admitted  the  doctrine  of  Lamarck  to  be  applicable  to 
the  evolution  of  the  types  of  unicellular  organisms. 
His  experiments  on  the  effect  of  temperature  on  the 
production  of  changes  of  color  in  butterflies,  showed 
that  such  changes  were  not  only  effected,  but  were 
sometimes  inherited.  This  he  endeavors  to  explain  as 
follows. 1  '  'Many  climatic  variations  may  be  due  wholly 
or  in  part,  to  the  simultaneous  variation  of  correspond- 
ing determinants  in  some  parts  of  the  soma  and  in  the 
germ-plasm  of  the  reproductive  cells."  This  is  an  ad- 
mission of  the  doctrine  which  in  1890  I  called  Diplo- 
genesis,2  and  which  is  adopted  in  the  present  work.  It 
appears  to  have  been  first  propounded  by  Galton  in 
1875.  In  the  chapter  on  Heredity  I  hope  to  offer  some 
reasons  for  believing  that  the  suggestion  of  Galton 
embraces  the  true  doctrine  of  heredity. 

From  what  has  preceded,  two  distinct  lines  of 
thought  explanatory  of  the  fact  of  organic  evolution 
may  be  discerned.  In  one  of  these  the  variations  of 
organisms  which  constitute  progressive  and  regressive 

1  The  Germ  Plasm,  Contemporary  Science  Series,  1893,  p.  406. 
^American  Naturalist,  Dec.,  1889;  published  in  1890. 


INTRODUCTION.  13 

evolution  appear  fortuitously,  and  those  which  are 
beneficial  survive  by  natural  selection,  while  those 
which  are  not  so,  disappear.  Characters  both  benefi- 
cial and  useless  or  harmless,  which  are  acquired  by  the 
adult  organism,  are  not  transmitted  to  the  young,  so 
that  no  education  in  habit  or  structure  acquired  by  the 
adult,  has  any  influence  in  altering  the  course  of  evo- 
lution. This  is  the  doctrine  of  Preformation.  From 
this  point  of  view  the  cause  of  the  variations  of  organ- 
isms has  yet  to  be  discovered. 

The  other  point  of  view  sees  in  variation  the  direct 
result  of  stimuli  from  within  or  without  the  organism  ; 
and  holds  that  evolution  consists  of  the  inheritance  of 
such  variations  and  the  survival  of  the  fit  through  nat- 
ural selection.  This  is  the  doctrine  of  Epigenesis.  To 
this  I  would  add  that  in  so  far  as  sensations  or  states 
of  consciousness  are  present,  they  constitute  a  factor  in 
the  process,  since  they  enable  an  organism  to  modify 
or  change  its  stimuli.  The  position  of  each  of  these 
schools  on  each  of  the  questions  to  which  reference 
has  been  made,  may  be  placed  in  opposition  as  follows  : 


1.  Variations  appear  in  defi- 
nite directions. 

2.  Variations  are  caused  by 
the  interaction  of   the   organic 
being  and  its  environment. 


3.  Acquired    variations    may 
be  inherited. 

4.  Variations  survive  directly 
as  they  are  adapted  to  changing 
environments.     (Natural   selec- 
tion.) 


i.  Variations  are  promiscu- 
ous or  multifarious. 

2.  Variations  are   "congeni- 
tal "  or  are  caused  by  mingling 
of  male  and  female  germ-plas- 
mas. 

3.  Acquired  variations  cannot 
be  inherited. 

4.  Variations  survive  directly 
as  they  are  adapted  to  changing 
environments.     (Natural    selec- 
tion.) 


i4     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


5.  Movements  of  the  organ- 
ism are  caused  or  directed  by 
sensation  and  other  conscious 
states. 


6.  Habitual    movements    are 
derived  from  conscious  experi- 
ence. 

7.  The  rational   mind   is  de- 
veloped by  experience,  through 
memory  and  classification. 


5.  Movements    of    organism 
are  not  caused  by  sensation  or 
conscious  states,  but  are  a  sur- 
vival through  natural  selection 
from   multifarious   movements. 

6.  Habitual    movements   are 
produced    by  natural    selection. 


7.  The  rational  mind  is  de- 
veloped by  natural  selection 
from  multifarious  mental  activ- 
ities. 


It  is  not  the  object  of  the  present  book  to  present  all 
the  available  evidence  on  both  sides  of  each  of  the  ques- 
tions above  enumerated.  I  propose  merely  to  submit 
certain  facts,  in  support  of  the  doctrines  contained  in 
the  left-hand  column  of  the  above  table.  My  aim  will 
be  to  show  in  the  first  place,  that  variations  of  charac- 
ter are  the  effect  of  physical  causes  ;  and  second,  that 
such  variations  are  inherited.  The  facts  adduced  in 
support  of  these  propositions  will  be  necessarily  prin- 
cipally drawn  from  my  own  studies  in  the  anatomy, 
ontology,  and  paleontology  of  the  Vertebrata.  It  will 
be  my  aim,  moreover,  to  co-ordinate  the  facts  of  evo- 
lution with  those  of  systematic  biology,  so  that  the  re- 
sult may  be  as  clearly  presented  as  possible.  The  fail- 
ure to  do  this  by  the  founders  of  evolutionary  doctrine 
has  given  their  work  a  lack  of  precision,  which  has 
been  felt  by  systematic  biologists.  The  detailed  ap- 
plication of  the  principles  of  Lamarck  and  Darwin  has 
been  the  work  of  their  successors,  and  has  necessarily 
thrown  much  new  light  on  the  principles  themselves. 
In  pursuing  the  object  above  stated,  I  shall  be  obliged 


INTR  OD  UCTION.  1 5 

to  consider  briefly  in  the  following  pages,  the  validity 
of  the  general  propositions  on  which  the  doctrine  of 
evolution  rests.  Less  space  will  be  given,  however, 
to  those  which  are  less  relevant,  than  to  those  which 
are  more  relevant  to  the  doctrine  of  neo-Lamarckism. 


PART  I. 


THE  NATURE  OF  VARIATION, 


PRELIMINARY. 


THE  structural  relations  of  organisms  may  be  ex- 
pressed in  the  following  canons  : 1 

1.  Homology. — This  means  that  organic  beings  are 
composed  of  corresponding  parts ;  that  the  variations  of 
an  original  and  fixed  number  of  elements  constitute 
their  only  differences.     A  part  large  in  one  animal  may 
be  small  in  another,  or  vice  versa  ;  or  complex  in  one 
and  simple  in  another.     The  analysis  of  animals  with 
skeletons,  or  Vertebrata,  has  yielded  several  hundred 
original  elements,  out  of  which  the  twenty-eight  thou- 
sand included  species  are  cpnstructed.      The  study  of 
homologies  is  thus  an  extended  one,  and  is  far  from 
complete  at  the  present  day. 

2.  Successional  Relation. — This   expresses   the   fact 
that  species  naturally  arrange  themselves  into  series  in 
consequence  of  an  order  of  excess  and  deficiency  in 
some  feature  or  features.     Thus  species  with  three  toes 
naturally  intervene  between  those  with  one  and  four 
toes.     So  with  the  number  of  chambers  of  the  heart, 
of  segments  of  the  body,  the  skeleton,  etc.     There  are 
greater  series  and  lesser  or  included  series,  and  mis- 
takes are  easily  made  by  taking  the  one  for  the  other. 

1  Origin  of  the  Fittest,  p.  6.     The  laws  here  stated  are  as  expressive  of  the 
relations  of  plants  as  of  animals. 


20    PRIMA  RY  FAC  TORS  OF  OR  CAN  1C  E  VOL  UTION. 

3.  Parallelism. — This  states  that  all  organisms  in 
their  embryonic  and  later  growth  pass  through  stages 
which  recapitulate  the  successive  permanent  condi- 
tions of  their  ancestry.     Hence  those  which  traverse 
fewer  stages  resemble  or  are  parallel  with  the  young  of 
those  which  traverse  more  numerous  stages.     This  is 
the  broad  statement,  and  is  qualified  by  the  details. 

4.  Teleology. — This  is  the  law  of  fitness  of  structures 
for  their  special   uses,   and  it  expresses  broadly  the 
general  adaptations   of  an  animal    to    its  home  and 
habits. 

The  first  and  fourth  of  the  laws  above  enumerated 
are  taken  for  granted  as  generally  accepted,  and  are 
not  especially  considered  in  the  following  pages.  The 
second  law,  that  of  successional  relation,  is  discussed 
and  illustrated  under  the  two  heads  of  Variation  and 
Phylogeny;  the  first  expressing  contemporary  relations, 
and  the  second,  successive  relations  in  time.  The  third 
law,  or  that  of  parallelism,  is  considered  in  a  chapter 
devoted  to  that  subject. 


CHAPTER  I— ON  VARIATION. 


PRELIMINARY. 

«•  ,  *      «•  •     '-  J      *        *•>"* 

A  LL  species  are  not  equally  variable.  Some  species 
jLJL  vary  little  or  not  at  all,  even  under  domestication. 
Thus  the  varieties  of  the  turkey  (Meleagris  gallopavd) 
and  the  guinea-fowl  (Numida  meleagris}  are  few,  and 
are  confined  to  albinistic  or  melanistic  conditions. 
The  barnyard  fowl  (Gallus  j/.),  on  the  other  hand, 
varies  enormously,  as  does  also  the  pigeon  (Columba 
livid).  Among  domesticated  Mammalia  the  variations 
of  cats  (Felts  domestica)  are  few  as  compared  with  those 
of  dogs  (Cam's  sp.}.  Variability  is  not  peculiar  to  do- 
mesticated animals.  A  large  proportion  of  animals 
and  plants  are,  in  a  state  of  nature,  variable,  and  some 
of  these  are  much  more  so  than  others.  The  common 
garter-snake  (Eut&niasirtalis}  varies  exceedingly,  while 
the  variations  of  the  allied  ribband  snake  (Eutania 
saurita)  are  minute  or  none.  But  little  variation  has 
been  observed  in  the  polar  bear  ([/rsus  maritimus), 
while  the  common  bear  (17.  arctos)  presents  many  vari- 
eties. Similar  conditions  are  found  among  fishes.  Thus 
the  larger  species  of  pike,  the  muskallonge  (Lucius  nobi- 
lior),  the  pike  (Z.  estor),  and  the  pickerel  (L.  vermicu- 
latus)  are  constant  in  their  characters,  whiIeTrie~small 
pickerel  (L.  vermiculatus)  presents  numerous  varieties. 


22     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

Many  of  the  varieties  of  the  animals  referred  to  in- 
habit the  same  territory,  although  some  are  restricted 
to  particular  regions.  Of  geographical  varieties  or 
races  much  is  known.  As  a  rule,  all  widely  distributed 
species  present  them.  Examples  are  the  brown  bear  of 
the  Northern  Hemisphere  (  Ursus  arctos) ;  the  cobra  di 
capello  snake  of  the  warmer  parts  of  Asia  {Naja  tripu- 
dians},  and  that  of  Africa  {Naja  haje}.  In  North  Amer- 
ica the  king-snake  (Ophibolus  getulus)  and  the  milk- 
snake  {Osceola  -doliatd}  are  represented  by  distinct 
faces  in  different  regions.  On  the  other  hand,  the 
copperhead  (Ancistrodon  contortrix)  and  the  Eastern 
rattlesnake  (Crotalus  horridus),  which  have  a  wide 
range,  scarcely  vary  at  all.  The  chub  {Hybopsis  bigut- 
tatus}  is  an  example  of  a  fish  distributed  everywhere 
east  of  the  Rocky  Mountains,  which  presents  scarcely 
any  variation. 

Variations  are  not  promiscuous  or  multifarious,  but 
are  of  certain  definite  kinds  or  in  certain  directions. 
Thus  amid  all  their  varieties,  dogs  never  present  black 
cross-bands  on  the  back  like  those  of  the  dog-opossum 
(Thylacinus  cynocephalus}  of  Tasmania,  nor  do  they 
present  ocellated  spots  like  those  of  the  leopard,  nor 
longitudinal  stripes  like  those  of  certain  squirrels.  The 
same  is  true  of  the  many  varieties  of  cattle  (Bos  tau- 
rus),  and  of  numerous  other  mammalia.  Domestic 
fowls  never  vary  to  blue  or  green,  colors  which  are 
common  to  many  other  birds ;  nor  are  canaries  known 
to  produce  blue  or  red  natural  sports.  All  variations 
are  in  the  first  place  necessarily  restricted  by  the  ex- 
isting characters  of  the  ancestor;  but  beyond  this  it  is 
evident  that  other  conditions  determine  the  nature  of 
the  variation.  It  is  not  supposable,  for  instance,  that 
the  pale  tints  of  animals  which  live  in  dry  regions 


ON  VARIATION.  23 

originated  by  an  accident  or  without  a  determining 
cause.  The  increased  amount  of  dark  pigment  ob- 
served in  animals  which  dwell  in  especially  humid  re- 
gions must  have  a  corresponding  cause,  and  it  is  nat- 
urally to  be  supposed,  of  a  kind  the  opposite  of  that 
which  produces  the  pale  colors. 

I  shall  adduce  some  illustrations  which  show  that 
color  variations  in  species,  as  well  as  structural  varia- 
tions in  higher  groups,  have  appeared  in  certain  defi- 
nite series,  and  observe  a  successional  relation  to  each 
other,  which  may  or  may  not  coincide  with  geograph- 
ical conditions.  The  same  relation  is  observed  in  the 
order  of  appearance  of  variations  on  the  body. 

Eimer  and  Weismann  have  shown  that  the  grad- 
ual modification  of  color  markings  has  originated  in 
lizards  and  in  caterpillars  at  the  posterior  end  of  the 
body  and  has  gradually  extended  forwards.  This  has 
been  discovered  both  by  comparisons  of  the  variations  of 
the  adults,  and  by  studies  of  the  order  of  their  appear- 
ance in  ontogenetic  growth.  Eimer  shows  that  longi- 
tudinal bands  have  been  produced  in  some  animals  by 
the  confluence  of  spots  placed  in  transverse  series, 
which  themselves  are  the  remains  of  interrupted  trans- 
verse bands.  Thus  he  believes  that  the  spots  of  the 
leopard  group  of  the  large  cats  were  derived  from  the 
breaking  up  of  transverse  bands  of  the  character  of 
those  now  possessed  by  the  tiger.  The  uniform  colo- 
ration of  the  lion  is  the  result  of  the  obliteration  of  the 
spots.  Traces  of  these  spots  may  be  distinctly  seen  in 
lions'  cubs. 

In  plants  variation  is  said  to  be  equally  definite  by 
Henslow.  He  says  :  "In  1847  Professor  J.  Buckman 
sowed  the  seed  of  the  wild  parsnip  in  the  garden  of 
the  Agricultural  College  at  Cirencester.  The  seeds 


24     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

began  to  vary,  but  in  the  same  way,  though  in  differ- 
ent degrees.  By  selecting  seed  from  the  best  rooted 
plants  the  acquired  ' somatic'  characters  of  an  en- 
larged root,  glabrous  leaves,  etc. ,  became  fixed  and 
hereditary;  and  the  ' Student,'  as  he  called  it,  having 
been  '  improved '  by  Messrs.  Sutton  and  Sons,  is  still 
regarded  as  '  the  best  in  the  trade. '  This  is  definite 
variation,  according  to  Darwin's  definition,  for  those 
weeded  out  did  not  differ  from  the  selected,  morpho- 
logically, except  in  degree,  the  variations  towards  im- 
provement not  being  quite  fast  enough  to  entitle  them 
to  survive.'* 

Finally  I  wish  especially  to  point  out  that  variation 
in  animals,  and  probably  in  plants,  (with  which  I  am 
not  so  familiar,)  gives  no  ground  for  believing  that 
"sports  "have  any  considerable  influence  on  the  course 
of  evolution.  This  is  apparent  whether  we  view  the 
serial  lines  of  variations  of  specific,  generic,  or  higher 
characters  ;  or  whether  we  trace  the  phylogeny  of  the 
animal  and  vegetable  types  by  means  of  the  paleonto- 
logical  record.  The  method  of  evolution  has  appar- 
ently been  one  of  successional  increment  or  decrement 
of  parts  along  definite  lines.  More  or  less  abruptness 
in  some  of  the  steps  of  this  succession  there  may  have 
been  ;  since  a  definite  amount  of  energy  expended  in 
a  given  direction  at  a  given  point  of  history  might  pro- 
duce a  much  greater  effect  than  the  same  amount  ex- 
pended at  some  other  period  or  point  of  evolution. 
This  might  be  due  to  the  release  of  stored  energy, 
which  could  only  be  accomplished  by  a  coincidence  of 
circumstances.  A  simple  illustration  of  the  phenome- 
non of  abrupt  metamorphosis  is  to  be  found  in  the 
passage  of  matter  from  the  gaseous  to  the  liquid,  and 


ON  VARIATION.  25 

from  the  liquid  to  the  solid  state.     I  have  stated  the 
case  in  the  following  language : 1 

"As  one  or  more  periods  in  the  life  of  every  spe- 
cies is  characterized  by  a  greater  rapidity  of  develop- 
ment "  (ontogenetic)  "  than  the  remainder  ;  so  in  pro- 
portion to  the  approximation  of  such  a  period  to  the 
epoch  of  maturity  or  reproduction  is  the  offspring 
liable  to  variation.  During  the  periods  corresponding 
to  those  between  the  rapid  metamorphoses,  the  char- 
acters of  the  genus  would  be  preserved  unaltered, 
though  the  period  of  change  would  be  ever  approach- 
ing. Hence  the  transformation  of  genera  may  have 
been  rapid  and  abrupt,  and  the  intervening  periods  of 
persistency  very  long.  Thus,  while  change  is  really 
progressing,  the  external  features  remain  unchanged 
at  other  than  those  points,  which  may  be  called  ex- 
pression points.  Now  the  expression  point  of  a  new  gen- 
eric type  is  reached  when  its  appearance  in  the  adult 
falls  so  far  prior  to  the  period  of  reproduction  as  to 
transmit  it  to  the  offspring  and  their  descendants. " 

i.  VARIATIONS  OF  SPECIFIC  CHARACTERS. 
a.    Variations  in  the  Coleopterous  Genus  Cicindela. 

Dr.  George  H.  Horn  has  traced  the  variations  in 
the  color  patterns  of  the  elytra  of  the  North  American 
species  of  this  abundant  and  well-known  genus.  He 
shows  that  they  form  series,  in  the  following  language  :2 

"Any  one  in  glancing  over  this  series  will  perceive 
that  there  is  a  great  similarity  of  marking  between 
many  species.  This  similarity,  which  may  be  con- 
sidered as  the  type  of  marking,  and  is  illustrated  by 

1  Origin  of  the  Fittest,  p.  79. 

2  Entomological  New s,  Philadelphia,  Feb.,  1892,  p.  25. 


26    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

No.  i  of  the  accompanying  plate  (Fig.  i)  is  the  under- 
lying pattern  from  which  all  the  forms  observed  in  our 
Cicindela  have  been  derived. 

"Before  going  further  it  is  well  to  present  the  fol- 
lowing propositions  that  the  argument  and  the  illus- 
trations may  be  understood. 

"i.  The  type  of  marking  is  the  same  in  all  our  spe- 
cies. 

"2.  Assuming  a  well-marked  species  as  a  central 
type  the  markings  vary, 

a,  by  a  progressive  spreading  of  the  white, 

b,  by  a  gradual  thinning  t>r  absorption  of  the  white, 
<r,  by  a  fragmentation  of  the  markings, 

d,  by  linear  supplementary  extension. 
"3.   Many  species  are  practically  invariable.   These 
fall  in  two  series, 

a,  those  of  the  normal  type,  as  vulgaris,  htrticollis, 
and  tenuisignata, 

b,  those  in  which  some  modification  of  the  type 
has  become  permanent,  probably  through  isolation,  as 
marginipennis,  togata,  and  lemniscata. 

.  "4.  Those  species  which  vary,  do  so  in  one  direc- 
tion only.  That  is,  supposing  a  species  begins  typ- 
ically with  markings  similar  to  vulgaris,  the  variation 
may  be  either  in  the  direction  of  thickening  and  in- 
crease of  white,  as  in  hyperborea,  generosa,  and  others, 
or  in  the  direction  of  thinning  or  fragmentation  of  the 
white  with  perhaps  an  entire  loss  of  markings  as  in 
hcemorrhagica,  splendida,  or  obsoleta. 

"The  first  two  propositions  must  be  considered  as 
applying  to  the  species  of  the  genus  collectively,  the 
last  two  to  the  species  separately. 

"The  accompanying  plate  has  been  prepared  to 
illustrate  these  propositions.  It  must,  however,  be 


ON  VARIATION. 


Fig.  i.— Horn  on  Cicindela. 


28    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

understood  that,  in  tracing  the  derivations  from  the 
typical,  it  is  not  possible  to  use  one  species,  as  these 
modifications  go  on  gradually  through  a  number  of 
species,  one  sometimes  beginning  where  another  ends. 
'  In  the  plate,  No.  i  represents  vulgarts,  which  is 
a  fairly  typical  species,  following  through  generosa 
(2-3),  pamphila  (4),  hyperborea  var.  (5),  togata  (6),  gra- 
tiosa  (7),  canosa  (8),  we  finally  arrive  at  a  perfect  white 
elytron  as  seen  in  some  varieties  of  dorsalis. 

"Following  in  the  other  direction  through  tenui- 
signata  (9),  marginipennis  (10),  hentzii  (n),  sexguttata 
(12),  hcemorrhagica  (13),  and  splendida  var.  (14),  it  will 
be  observed  that  through  a  gradual  thinning  or  ab- 
sorption of  the  markings,  or  by  their  fragmentation 
and  obliteration,  we  arrive  at  the  opposite  result  of 
elytra  without  any  white  markings  whatever,  as  in 
many  forms  of  obsoleta,  scute  liar  is,  punctulata,  and  Juz- 
morrhagica. 

"Those  species  which  vary  from  the  type  in  hav- 
ing the  markings  broken  into  spots,  as  in  \2-guttata 
or  hentzii,  may  lose  the  spots  by  a  gradual  decrease  of 
size,  so  that  they  all  seem  to  disappear  nearly  at  the 
same  time ;  or  the  spots  may  disappear  successively, 
those  on  the  disc  being  the  first  to  go,  while  the  mar- 
ginal spots  remain. 

"  From  our  series  it  would  be  difficult  to  say  which 
spot  is  the  most  persistent,  but  it  is  probably  the  lu- 
nule,  as  there  are  more  with  entirely  dark  elytra  with 
slight  traces  of  this  spot  than  with  any  other,  as  shown 
in  abdominalis  and  punctulata. 

"Forms  like  lemniscata  (16)  seem  very  far  removed 
from  the  type,  but  many  forms  of  imperfecta  (15)  show 
how  the  markings  gradually  leave  the  margin  and  tend 


ON  VARIATION.  29 

by  fusion  to  form  a  vitta  at  first  somewhat  oblique, 
but  finally  becoming  nearly  median. 

"The  last  two  figures  on  the  plate  represent  the 
markings  of  gabbii  (17)  and  saulcyi  (18),  in  which  the 
ends  of  the  bands  or  lunules  are  greatly  prolonged. 
The  latter  form,  which  represents  dorsalis  as  well,  is 
but  rarely  seen  so  perfectly  marked,  the  tendency  being 
toward  a  greater  extension  of  the  white.  The  other 
species  is  scarcely  variable,  although  equally  a  coast 
form. 

"Those  species  which  retain  a  permanent  diver- 
gence from  the  normal  standard,  such  as  togata  (6)  or 
lemniscata  (16),  are  doubtless  descendants  from  a  nor- 
mal type  which  has  varied,  and  in  which  a  variety  has 
become  isolated  and  perpetuated  itself." 

The  accompanying  plate  is  copied  from  the  original 
drawing  by  Dr.  Horn,  and  which  accompanies  the 
paper  now  cited. 

b.    Variations  in  the  Osceola  doliata. 

The  Milk-Snake,  Osceola  doliata  Linn.,  ranges  in 
North  America  over  the  Eastern,  Central,  and  Austro- 
riparian  districts,  and  is  absent  from  the  Sonoran 
and  Pacific  districts.  It  is  found  also  in  the  humid 
regions  of  Mexico  and  Central  America,  as  far  as  the 
Isthmus  of  Darien.  Beyond  this  point  it  does  not  oc- 
cur, but  a  very  similar  snake  (Opheomorphus  mtmus)  is 
found  in  New  Grenada. 

I  have  called  attention  to  the  color  variations  of 
this  species  in  a  brief  paragraph  in  the  introduction  to 
my  check  list  of  Batrachia  and  Reptilia  in  North 
America,  1875,*  and  have  given  the  characters  of  the 

1  Bulletin  of  the  U.  S.  National  Museum,  No.  I,  p.  4. 


30     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

color  types,  or  subspecies,  in  an  analytical  key,  in  a 
"Review  of  the  Characters  and  Variations  of  the 
Snakes  of  North  America,"  I892.1  I  have  also  given  a 
series  of  figures  representing  the  North  American  color 
forms,  for  which  I  am  indebted  to  the  United  States 
National  Museum,  which  are  here  reproduced. 

Before  going  further  into  the  patterns  of  the  Osce- 
ola  doliata,  I  give  a  synoptic  key  of  them. 

I.  No  yellow  band  posteriorly  from  orbit  (a  yellow  half-collar). 
a.  Dorsal  spots  or  saddles  (red)  open  at  the  side,  the  borders  of 
adjacent  spots  forming  pairs  of  black  rings. 

Interspaces  between  red  saddles  open  below  ;  scales  not 
black-tipped  ;  front  more  or  less  black  ;  first  black  ring 
on  nape  only  :  O.  d.  coccinea. 

Interspaces  between  red  saddles  closed  by  black  spot  be- 
low ;  scales  black  tipped  ;  front  black  ;  first  black  ring 
complete  :  O.  d.  polyzona. 

Interspaces  not  closed  ;  rings,  including  first,  complete  on 
belly;  first  yellow  band  crossing  occipital  plates;  front 
black  ;  scales  not  black-tipped  :  O.  d.  conjuncta. 

aa.  Dorsal  spots  closed  at  the  sides  below,  forming  saddles. 
b.  Saddles  closed  by  a  single  black  tract  on  the  middle  of  the 
belly;  no  spots  between  the  saddles. 

Dorsal  spots  undivided  medially;  front  black  ;  first  black 

ring  complete  :  O.  d.  annulata. 

Dorsal  spots  divided  longitudinally  by  a  median  black 

connection  ;  front  black  :  O.  d.  gentilis. 

bb.  Inferior  borders  of  saddles  separate  and  not  confluent  with 

each  other. 

Saddles  completed  on  gastrosteges  ;  no  alternating  spots  ; 
no  black  collar  :  O.  d.  parallela. 

Saddles  completed  on  gastrosteges  ;  spots  opposite  inter- 
vals forming  a  single  series  on  the  middle  line  of  the 
belly  :  O.  d.  syspila. 

Saddles  completed  above  the  gastrosteges ;  alternating 
spots  which  do  not  meet  on  the  middle  line  of  the  belly: 

O.   d.  do  Hat  a. 

\Proceedingsofthe  U.  S.  National  Museum,  XIV,  p.  589-608. 


ON  VARIATION.  31 

II.  A  yellow  band  posteriorly  from  orbit,  bounded  below  by  a  black 

or  brown  one. 

a.  Saddle  spots  closed  laterally  on  gastrosteges  ;  alternate  spots 
entirely  on  gastrosteges. 

A  half  collar   behind   parietal   plates,    no   superciliary 
stripe  :  O.  d.  temporalis. 

aa.  Saddle  spots  closed  above  gastrosteges ;  alternate  spots  on 
scales. 

A  half  collar  nearly  or  quite  touching  occipital  plates,  no 
bands  ;  alternate  spots  partly  on  gastrosteges  : 

O.  d.  co  liar  is. 

Neck  with  longitudinal  bands  ;  alternate  spots  partly  on 
gastrosteges  •„  O.  d.  clerica. 

Neck  with  bands  ;  alternate  spots  entirely  on  scales  : 

O.  d.  triangula. 

In  Fig.  2  are  represented  vertical,  lateral,  and  in- 
ferior views  of  parts  of  the  body  of  the  subspecies  tri- 
angula, taken  from  a  specimen  in  my  collection  from 
Westchester  County,  New  York,  which  I  owe  to  the 
kindness  of  my  friend,  Mr.  T.  H.  Mead. 

The  characters  of  this  form  are  seen  in  (i)  the 
presence  of  a  light  band  extending  from  the  posterior 
angle  of  the  eye  downward  and  backward,  which  is 
bounded  by  a  black  border  above  and  below ;  (2)  a 
black  cross-band  on  the  posterior  border  of  the  pre- 
frontal  plates;  (3)  chevron  shaped  mark  with  the  apex 
on  the  posterior  part  of  the  frontal  plate,  whose  limbs 
extend  posteriorly  as  a  band  on  each  side  of  the  neck, 
where  they  are  fused  together,  and  continue  as  a  sin- 
gle, broad  band  for  a  short  distance ;  (4)  a  series  of 
lateral  spots  which  do  not  extend  beyond  the  scales  on 
to  the  gastrosteges,  and  which  alternate  with  the  dor- 
sal spots ;  (5)  a  series  of  spots  on  the  ends  of  the  gas- 
trosteges which  alternate  with  the  last  mentioned; 
(6)  a  series  of  spots  on  the  centers  of  the  gastrosteges 
which  alternate  with  the  spots  mentioned  under  (5). 


32     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


Fig.  2.     Osceola  doliata  triangula. 


Fig.  3.     Osceola  doliata  clerica. 


ON  VARIATION,  33 

The  ground  color  in  this  form  is  gray,  and  the  spots 
are  a  rich  brown  with  black  borders.  The  belly  has  a 
white  ground  color. 

In  Fig.  3  we  have  the  subspecies  clerica,  where 
the  following  modifications  appear.  The  fusion  of  the 
limbs  of  the  chevron  is  more  complete,  and  the  dorsal 
spots  are  more  expanded  transversely.  They  extend 
to  within  two  or  three  scales  of  the  gastrosteges,  while 
in  the  form  triangulus  they  are  five  scales  distant.  The 
alternate  spots  touch  the  gastrosteges.  This  figure  is 
taken  from  a  specimen  in  the  Museum  of  the  Phila- 
delphia Academy  from  southern  Illinois. 

In  Fig.  4  we  have  an  individual  from  Elmira,  Illi- 
nois, which  illustrates  the  characters  of  the  form  col- 
lar is.  Here  the  chevrons  are  distinct  from  the  first 
dorsal  spot,  whose  anterior  black  border  forms  a  half 
collar  on  the  neck.  This  specimen  is  instructive,  as 
it  displays  the  last  connection  between  the  chevron 
and  the  first  spot,  in  a  black  line  on  each  side.  This 
is  wanting  in  the  typical  ccllaris. 

The  collar  of  ground  color  is  complete  in  its  an- 
terior border,  as  well  as  the  posterior  in  the  form  tem- 
poralis  (Fig.  5),  owing  to  the  disappearance  of  the 
chevron.  The  transverse  band  on  the  prefrontals  has 
also  disappeared.  The  anterior  extremity  of  the  post- 
orbital  stripe  is  cut  off,  and  consists  of  a  spot  of  ground 
color.  The  dorsal  saddle  spots  are  wider,  reaching  the 
gastrosteges,  while  the  intermediate  spots  are  exclu- 
sively gastrostegal.  The  spots  which  alternate  with 
them,  have  fused  on  the  middle  line.  Fig.  5  is  from 
a  specimen  from  the  State  of  Delaware. 

In  subspecies  doliata  the  postocular  stripe  has  dis- 
appeared, and  the  chevron  is  replaced  by  a  black  patch 
on  the  parietal  and  temporal  plates.  In  other  respects 


34     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


Fig.  4.     Osceola  doliata  collaris. 


Fig.  5.      Osceola  doliata  temporalis. 


ON  VARIATION.  35 

this  form  is  more  like  the  form  collaris.  The  dorsal 
saddle  spots  are  separated  by  a  row  or  two  of  scales 
from  the  gastrosteges,  and  their  alternating  spots  are 
partly  on  the  scales.  The  ground  color  in  this  form, 
as  in  the  temporalis,  approaches  red.  This  is  the  form 
of  the  tier  of  states  between  latitude  40°  and  the  Gulf 
States. 

The  subspecies  syspila  is  represented  in  Fig.  8. 
The  head  pattern  is  like  that  of  doliata  with  the  black 
patch  more  or  less  reduced — in  the  specimen  figured 
being  represented  by  a  cross  stripe.  The  dorsal  saddle 
spots  are  more  expanded  than  in  any  form  yet  encoun- 
tered, their  lateral  borders  being  completed  below  the 
scales  and  entirely  on  the  gastrosteges.  The  alternate 
spots  now  meet  and  fuse  on  the  middle  line  of  the  ab- 
domen, and  the  second  series  of  alternating  spots  has 
disappeared.  This  is  distinctively  a  southern  form, 
extending  west  to  central  Oklahoma. 

The  dorsal  saddles  are  so  far  extended  in  the  next 
subspecies,  parallela,  as  to  form  two  parallel  stripes 
with  a  narrow  strip  of  ground  color  between,  on  the 
middle  line  of  the  abdomen.  The  alternating  spots 
have  disappeared.  In  the  specimen  figured,  which  is 
from  Florida,  and  is  in  the  United  States  National 
Museum,  the  supraocular  spots  seen  in  temporalis,  are 
indicated.  The  ground  color  is  red.  Black  begins  to 
appear  on  the  head. 

From  the  form  syspila  two  types  of  color  modifica- 
tion may  be  traced.  One  of  these  brings  the  borders 
of  the  saddle  spots  together  on  the  median  line,  form- 
ing a  median  black  stripe  ;  this  is  the  subspecies  annu- 
lata,  which  belongs  to  western  Texas  and  the  adjacent 
parts  of  Mexico.  The  top  of  the  head  is  black  (Fig. 
10).  In  the  other,  the  lateral  borders  of  the  saddle 


36     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


Figs.  6-7.     Osceola  doliata  doliata. 


ON  VARIATION.  37 

spots  have  disappeared  altogether,  so  that  the  body  is 
more  or  less  completely  encircled  by  pairs  of  black 
rings,  the  alternating  spots  having  disappeared.  This 
might  be  supposed  to  have  resulted  from  a  continua- 
tion of  the  process  by  which  the  alternating  spots  have 
disappeared,  and  the  edges  of  the  saddles  been  brought 
closer  and  closer  together.  The  continued  transverse 
extension  of  the  spot  color  would  finally  obliterate  the 
lateral  borders  completely,  as  actually  occurs  in  this 
last  form,  the  coccinea  of  authors,  which  is  the  com- 
mon type  of  the  Gulf  Coast.  But  the  black  has  not 
covered  the  head  and  muzzle  of  this  form  as  in  the  an- 
nulata.  These  regions  are  on  the  contrary  red,  as  is 
the  spot  color  generally,  while  the  ground  color  is  pale 
yellow. 

A  tendency  to  a  development  of  black  pigment  in 
the  saddle  spots  is  seen  in  two  other  forms.  The  sub- 
species gentilis  resembles  annulata,  but  has  a  black 
longitudinal  dorsal  band  which  divides  each  saddle 
spot  in  two  equal  halves.  This  is  a  rare  form,  only 
known  from  the  Indian  Territory.  The  common  Mex- 
ican form  (J)olyzond)  has  the  paired  rings  of  coccinea, 
the  black  head  of  annulata,  but  each  scale  of  the  red 
intervals  is  tipped  with  black. 

The  relations  of  these  forms  may  be  expressed  in  a 
tabular  form,  given  on  page  39. 

The  main  series  corresponds  with  a  distribution  in 
latitude,  commencing  with  the  triangula  of  New  Eng- 
land and  New  York,  and  passing  gradually  to  the  coc- 
cinea of  the  Gulf  Coast  regions,  and  polyzona  of  Mex- 
ico and  Central  America.  The  forms  of  the  right-hand 
column  are  (except  the  parallela)  from  the  central 
warmer  parts  of  the  continent. 

This  series  of  color-forms  of  the    Osceola  doliata 


38     PRIM  A  K  Y  FA  CTORS  OF  ORGANIC  E  VOL  UTION. 


Fig.  8.     Osceola  doliata  syspila. 


Fig.  9.     Osceola  doliata  par allcla. 


ON  VARIATION. 


39 


demonstrates  the  following  points.  First :  the  color- 
variation  is  determinate  and  not  indeterminate.  It 
consists  in,  a,  the  successive  enlargement  of  the  dorsal 
spots  toward,  to,  and  across,  the  belly;  b,  the  diminu- 
tion and  extinction  of  the  longitudinal  stripes  on  ..the 
head  ;  c,  do.  of  the  spots  of  the  inferior  surface  of  the 
body ;  d,  in  the  increase  of  red  in  the  color  of  the 
dorsal  spots,  coincidentally  with  the  changes  men- 
tioned. Second  :  these  color-changes  follow  parallels 


polyzona 


conjuncta 


gentilis 


annulata 


parallela 


syspila 


doliata 


collaris 
clerica 

I 

triangula 

of  latitude,  the  red  color  and  accompanying  changes 
developing  from  north  to  south.  Third  :  so  far  as  re- 
gards eastern  North  America,  there  is  a  diminution  of 
size  in  passing  from  north  to  south  ;  the  O.  d.  coccinea 
being  the  smallest  of  the  subspecies.  In  Mexico,  the 
size  is  recovered,  as  the  O.  d.  polyzona  equals  in  di- 
mensions the  O.  d.  triangula. 

The  young  of  the  northern  O.  d.  triangula  pre- 
sents the  colors  of  the  dorsal  spots  nearly  as  brilliant 
as  those  of  the  southern  O.  d.  coccinea,  and  they  fade 


40     PR  I  MAR  Y  FA  CTORS  OF  OR  GANIC  E  VOL  UTION. 


Fig.  10.     Osceola  doliata  annulata. 


Fig.  ii.     Osceola  doliata  coccinea. 


ON  VARIATION.  41 

with  age  to  the  adult  character.  The  pattern  in  the 
young  at  the  period  of  hatching  is  the  same  as  that  of 
the  adult. 

>*.    Color-  Variations  in  Cnemidophorus. 

Another  illustration  of  the  nature  of  color-variation 
is  to  be  found  in  certain  species  of  the  lacertilian  gen- 
era Cnemidophorus  in  America,  and  Lacerta  in  Eu- 
rope. In  both  genera  the  color-markings  differ  in  the 
same  individual  at  different  ages,  and  the  age  at  which 
the  adult  coloration  is  assumed,  differs  in  different  lo- 
calities. Some  of  the  species,  e.  g.,  Cnemidophorus 
sexlineatus,  never  abandon  the  coloration  of  the  young 
of  other  species  and  subspecies.  The  same  condition 
is  characteristic  of  the  C.  deppei  of  Mexico,  the  C.  lem- 
niscatus  of  Brazil,  and  other  species.  The  process  of 
color-modification  in  the  C.  tessellatus  and  C.  gularis 
of  North  America  is,  as  I  have  pointed  out,1  as  follows : 
The  young  are  longitudinally  striped  with  from  two  to 
four  stripes  on  each  side  of  the  middle  line.  With  in- 
creasing age,  light  spots  appear  between  the  stripes 
in  the  dark  interspaces.  In  a  later  stage  these  spots 
increase  in  transverse  diameter,  breaking  up  the  dark 
bands  into  spots.  In  some  of  the  forms  these  dark 
spots  extend  themselves  transversely  and  unite  with 
each  other,  forming  black  cross-stripes  of  greater  or 
less  length.  Thus  we  have  before  us  the  process  by 
which  a  longitudinally  striped  coloration  is  transformed 
into  a  transversely  striped  one. 

The  large  number  of  specimens  of  the  C.  tessellatus 
and  C  gularis  in  the  National  Museum  collection  show 
that  the  breaking  up  of  the  striped  coloration  appears 

1  Proceeds.  Amer.  Philos.  Soc.,   1885,  p.  283.     Transac.  Amer.  Philos.   Soc 
1892,  p.  27. 


42     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


v  / 


ON  VARIATION. 


43 


first  at  the  posterior  part  of  the  dorsal  region  (i.  e.,  the 
sacral  and  lumbar).     The  confluence  of  the  spots  ap- 


pears  there  first;  and  finally  (C.  gularis  semifasciatus}, 
where  the  color  markings  disappear,  leaving  a  uniform 
hue,  this  also  appears  first  at  the  posterior  part  of  the 


44     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION, 


ON  VARIATION.  45 

body.  In  the  C.  tessellatus  rubidus  the  dark  spots  dis- 
appear first  on  the  anterior  regions. 

According  to  Eimer,1  among  many  color-variations 
of  the  Lacerta  muralis  there  exists  a  series  of  types 
closely  similar  to  those  observed  by  me  to  characterize 
the  two  species  of  Cnemidophorus  mentioned.  I  give 
figures  of  these  series  in  all  three  species.  It  will  be 
observed  that  in  the  second  and  third  forms  (B  and  C) 
of  the  L.  muralis,  the  pale  portions  of  the  dark  stripes 
do  not'assume  the  very  light  hue  of  the  ground  color 
as  they  do  in  the  corresponding  phase  of  the  Cnemido- 
phorus tessellatus  (C  and  D,  Fig.  12),  but  this  interme- 
diate condition  is  exactly  paralleled  by  the  subspecies 
mariarum  of  the  Cnemidophorus  gularis.  The  corre- 
spondences are  represented  in  the  table  on  page  46. 

There  are  some  color  forms  in  the  Lacerta  muralis 
which  are  not  repeated  in  the  North  American  Cnemi- 
dophori,  particularly  those  whidh  result  in  a  strong 
contrast  between  the  dorsal  colors  as  a  whole  and  the 
darker  lateral  colors,  as  a  band.  The  color  variety, 
No.  7,  of  the  Cnemidophori  is  not  reported  by  Eimer 
as  occurring  in  the  Lacerta  muralis. 

The  variations  from  one  to  four  form  a  direct  series, 
and  so  do  those  represented  by  Nos.  i,  2,  3,  and  5. 
Such  variations  cannot  be  regarded  as  promiscuous, 
especially  when  the  same  process  of  change  is  to  be 
observed  in  three  different  species,  one  of  which  in- 
habits a  continent  remote  from  the  other  two. 

d.   Variations  in  North  American  Birds  and  Mammals  in 
Relation  to  Locality. 

The  distinguished  zoologist,  Dr.  J.  A.  Allen  of  New 
York,  has  made  a  thorough  study  of  this  subject  with 

\ArchivfUr  Naturgeschichte,  1881,  p.  239. 


46    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


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ON  VARIATION.  47 

ample  material  at  his  disposal.  Following  lines  al- 
ready laid  down  by  Prof.  Spencer  F.  Baird,  Dr.  Allen 
has  shown  that  variations  in  form,  size,  and  color  are 
directly  related  to  latitude,  and  that  they  are  not  pro- 
miscuous or  multifarious,  but  are  definite  and  graded. 
I  make  the  following  extract  from  a  summary  of  the 
subject  published  by  him  in  The  Radical  Review  (New 
Bedford,  Mass.)  for  May,  1877: 

"Geographical  variation,  as  exhibited  by  the  mam- 
mals and  birds  of  North  America,  may  be  summarized 
under  the  following  heads,  namely  :  (i)  variation  in 
general  size,  (2)  in  the  size  of  peripheral  parts,  and 
(3)  in  color ;  the  latter  being  subdivisible  into  (a)  vari- 
ation in  color  with  latitude,  and  (/£)  with  longitude. 
As  a  rule,  the  mammals  and  birds  of  North  America 
increase  in  size  from  the  south  northward.  This  is 
true,  not  only  of  the  individual  representatives  of  each 
species,  but  generally  the  largest  species  of  each  genus 
and  family  are  northern.  There  are,  however,  some 
strongly  marked  exceptions,  in  which  the  increase  in 
size  is  in  the  opposite  direction,  or  southward.  There 
is  for  this  an  obvious  explanation,  as  will  be  presently 
shown ;  the  increase  being  found  to  be  almost  invari- 
ably toward  the  region  where  the  type  or  group  to 
which  the  species  belongs  receives  its  greatest  numer- 
ical development,  and  where  the  species  are  also  most 
specialized.  Hence  the  representatives  of  a  given  spe- 
cies increase  in  size  toward  its  hypothetical  center  of 
distribution,  which  is  in  most  cases  doubtless  also  its 
original  center  of  dispersal.  Consequently  there  is  fre- 
quently a  double  decadence  in  size  within  specific 
groups,  and  both  in  size,  and  numerically  in  the  case  of 
species,  when  the  center  of  development  of  the  group 
to  which  they  belong  is  in  the  warm-temperate  or  trop- 


48    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

ical  regions.  This  may  be  illustrated  by  reference  to 
the  distribution  of  the  higher  classes  of  vertebrates  in 
North  America.  Among  the  species  occurring  north  of 
Mexico  there  are  very  few  that  may  not  be  supposed  to 
have  had  a  northern  origin ;  and  the  fact  that  some 
are  circumpolar  in  their  distribution,  while  most  of  the 
others  (especially  among  the  mammals)  have  congeneric 
Old  World  allies  further  strengthens  the  theory  of  their 
northern  origin.  Not  only  do  individuals  of  the  same 
species  increase  in  size  toward  the  north,  but  the  same 
is  true  of  the  species  of  different  genera.  Again,  in 
the  exceptional  cases  of  increase  in  size  southward,  the 
species  belong  to  southern  types,  or,  more  correctly, 
to  types  having  their  center  of  development  within  or 
near  the  intertropical  regions,  where  occur,  not  only  the 
greatest  number  of  the  specific  representatives  of  the 
type,  but  also  the  largest. 

"For  more  detailed  illustration  we  may  take  three 
families  of  the  North  American  Carnivora;  namely, 
the  Canidae  (wolves  and  foxes),  the  Felidae  (lynxes 
and  wild  cats),  and  the  Procyonidae  (raccoons).  The 
first  two  are  to  some  extent  cosmopolitan,  while  the 
third  is  strictly  American.  The  Canidae  have  their 
largest  specific  representatives,  the  world  over,  in  the 
temperate  or  colder  latitudes.  In  North  America  the 
family  is  represented  by  six  species,1  the  smallest  of 
which  (speaking  generally)  are  southern,  and  the  larg- 
est northern.  Four  of  them  are  among  the  most  widely 
distributed  of  North  American  mammals,  two  (the 
gray  wolf  and  the  common  fox)  being  circumpolar  spe- 
cies ;  another  (the  Arctic  fox)  is  also  circumpolar,  but 

IThe  gray  wolf  (Cam's  lupus],  the  coyote  (C.  latrans),  the  Arctic  fox  (Vul- 
pes  lagopus) ,  the  common  fox  (V.  alopex],  the  kit  fox  (V.  velox],  and  the  gray 
fox  {V.  cinereoargentatus). 


ON  VARIATION.  49 

is  confined  to  high  latitudes.  The  three  widest-rang- 
ing species  (the  gray  wolf,  the  common  fox,  and  the 
gray  fox)  are  those  which  present  the  most  marked 
variation  in  size.  Taking  the  skull  as  the  basis  of 
comparison,  it  is  found  that  the  common  wolf  is  fully 
one-fifth  larger  in  the  northern  parts  of  British  Amer- 
ica and  Alaska  than  it  is  in  Northern  Mexico,  where  it 
finds  the  southern  limit  of  its  habitat.  Between  the 
largest  northern  skull  and  the  largest  southern  skull 
there  is  a  difference  of  about  thirty-five  per  cent,  of  the 
mean  size!  Specimens  from  the  intermediate  region 
show  a  gradual  intergradation  between  these  extremes, 
although  many  of  the  examples  from  the  upper  Mis- 
souri country  are  nearly  as  large  as  those  from  the  ex- 
treme North. 

"The  common  fox,  though  occurring  as  far  north 
as  the  wolf,  is  much  more  restricted  in  its  southward 
range,  especially  along  the  Atlantic  coast,  and  presents 
a  correspondingly  smaller  amount  of  variation  in  size. 
The  Alaskan  animal,  however,  averages  about  one- 
tenth  larger  than  the  average  size  of  specimens  from 
New  England.  In  the  gray  fox,  whose  habitat  ex- 
tends from  Pennsylvania  southward  to  Yucatan,  the 
average  length  of  the  skull  decreases  from  about  five 
inches  in  Pennsylvania  to  considerably  less  than  four 
in  Central  America — a  difference  equal  to  about  thirty 
per  cent,  of  the  mean  size  for  the  species. 

"The  Felidae,  unlike  the  Canidae,  reach  their  great- 
est development,  as  respects  both  the  number  and 
the  size  of  the  species,  in  the  intertropical  regions. 
This  family  has  but  a  single  typical  representative — 
the  panther  (Felis  concolor} — north  of  Mexico,  and  this 
ranges  only  to  about  the  northern  boundary  ot  the 
United  States.  The  other  North  American  represen- 


50     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

tatives  of  the  family  are  the  lynxes,  which,  in  some  of 
their  varieties,  range  from  Alaska  to  Mexico.  They 
form,  however,  the  most  northern,  as  well  as  the  most 
specialized  or  '  aberrant/  type  of  the  family.  While 
they  vary  greatly  in  color,  as  well  as  in  the  length  and 
texture  of  the  pelage,  at  different  localities,  they  afford 
a  most  remarkable  exception  to  all  laws  of  variation  in 
size  with  locality;  for  a  large  series  of  skulls,  repre- 
senting localities  as  widely  separated  as  Louisiana, 
Northern  Mexico,  and  California,  on  the  one  hand,  and 
Alaska  and  the  Mackenzie  River  district  on  the  other, 
as  well  as  various  intermediate  localities,  reveals  no  ap- 
preciable difference  in  size  throughout  this  wide  area. 
The  true  cats,  however,  as  the  panther  and  the  ocelots, 
are  found  to  greatly  increase  in  size  southward,  or  to- 
ward the  metropolis  of  the  family.  The  panther  ranges 
from  the  Northern  States  southward  over  most  of 
South  America.  Skulls  from  the  Adirondack  region  of 
New  York  have  an  average  length  of  about  seven  and 
a  half  inches,  the  length  increasing  to  eight  and  three- 
quarters  in  Louisiana  and  Texas,  from  beyond  which 
points  there  is  lack  of  data.  The  ocelot  (Felis  parda- 
lls)  finds  its  northern  limit  near  the  Rio  Grande  of 
Texas,  and  ranges  thence  southward  far  into  South 
America.  The  average  size  of  Costa  Rican  examples 
is  about  one-fifth  greater  than  that  of  specimens  from 
the  Rio  Grande. 

Instances  of  increase  in  size  northward  among  the 
Carnivora  of  North  America  are  so  generally  the  rule 
that  further  space  need  not  be  taken  in  recounting  ex- 
amples, in  detail.  It  may  suffice  to  state  that  the 
badger  (Taxidea  americand},  the  marten  (Mustela  ame- 
ricana],  the  fisher  (M.  pennanti},  the  wolverine  {Gulo 
luscus},  and  the  ermine  {Putorius  ermineus} — all  north- 


ON  VARIATION.  51 

ern  types — afford  examples  of  variations  in  size  strictly 
parallel  with  that  already  noticed  as  occurring  in  the 
foxes  and  wolves. 

"To  refer  briefly  to  other  groups,  it  may  be  stated 
that  the  Cervidae  (deer  family)  are  mainly  rather  north- 
ern in  their  distribution ;  that  the  largest  species  occur 
in  the  colder  zones,  and  that  individuals  of  the  same 
species  increase  rapidly  in  size  toward  the  north. 
Some  of  the  species,  in  fact,  afford  some  of  the  most 
striking  instances  of  northward  increase  in  size ;  among 
which  are  the  Virginia  deer  and  its  several  representa- 
tives in  the  interior  of  the  continent  and  on  the  Pacific 
Slope.  It  is  also  noteworthy  that  the  most  obviously 
distinctive  characteristic  of  the  group — the  large,  an- 
nually deciduous  antlers — reaches  its  greatest  devel- 
opment at  the  northward.  Thus  all  the  northern  spe- 
cies, as  the  moose,  the  elk,  and  the  caribou,  have 
branching  antlers  of  immense  size,  while  the  antlers 
are  relatively  much  smaller  in  the  species  inhabiting 
the  middle  region  of  the  continent,  and  are  reduced  to 
a  rudimentary  condition— a  simple,  slender,  sharp  spike, 
or  a  small  and  singly  forked  one — in  the  tropical  spe- 
cies; the  antlers  declining  in  size  much  more  rapidly 
than  the  general  size  of  the  animal.  This  is  true  in 
individuals  of  the  same  species  as  well  as  of  the  species 
collectively. 

"The  Glires  (the  squirrels,  marmots,  spermophiles 
mice,  and  their  affines)  offer  the  same  illustrations  in 
respect  to  the  law  of  increase  in  size  as  the  species 
already  mentioned,  the  size  sometimes  increasing  to 
the  southward,  but  more  generally  to  the  northward, 
since  the  greater  number  of  the  species  belong  decid- 
edly to  northern  types.  There  is  no  more  striking  in- 
stance known  among  mammals  of  variation  in  size 


52     PRIMAR  Y  FA  CTORS  OF  ORGANIC  E  VOL  UTION. 

with  locality  than  that  afforded  by  the  flying  squirrels, 
in  which  the  northern  race  is  more  than  one-half  larger 
than  the  southern ;  yet  the  two  extremes  are  found  to 
pass  so  gradually  the  one  into  the  other,  that  it  is 
hardly  possible  to  define  even  a  southern  and  a  north- 
ern geographical  race,  except  on  the  almost  wholly 
arbitrary  ground  of  difference  in  size.  The  species, 
moreover,  is  one  of  the  most  widely  distributed,  rang- 
ing from  the  Arctic  regions  (the  northern  limit  of  for- 
ests) to  Central  America. 

"Among  birds  the  local  differences  in  size  are  al- 
most as  strongly  marked  as  among  mammals,  and  in 
the  main,  follow  the  same  general  law.  A  decided 
increase  in  size  southward,  however,  or  toward  the 
warmer  latitudes,  occurs  more  rarely  than  in  mam- 
mals, although  several  well-marked  instances  are 
known.  The  increase  is  generally  northward,  and  is 
often  very  strongly  marked.  The  greatest  difference 
between  northern  and  southern  races  occurs'  as  in 
mammals,  in  the  species  whose  breeding-stations  em- 
brace a  wide  range  of  latitude.  In  species  which  breed 
from  Northern  New  England  to  Florida,  the  southern 
forms  are  not  only  smaller,  but  are  also  quite  different 
in  color  and  in  other  features.  This  is  eminently  the 
case  in  the  common  quail  {Ortyx  virgim'anus),  the 
meadow-lark  (Sturnella  magna~),  the  purple  grackle 
(jQuiscalus  purpurcus),  the  red- winged  blackbird  (Age- 
laeus  phaeniceus},  the  golden- winged  woodpecker  (Co- 
laptes  auratus^y  the  towhee  (Pipilo  erythrophthalmus}, 
the  Carolina  dove  (Zenczdura  macrura),  and  in  nu- 
merous other  species  ;  and  is  quite  appreciable  in  the 
blue-jay  (Cyanurus  cristatus},  the  crow  {Corvus  ameri- 
canus},  in  most  of  the  woodpeckers,  in  the  titmice, 
numerous  sparrows,  and  several  thrushes  and  war- 


ON  VARIATION.  53 

biers,  the  variation  often  amounting  to  from  ten  to 
fifteen  per  cent,  of  the  average  size  of  the  species. 

"As  a  general  rule,  certain  parts  of  the  organisms 
vary  more  than  does  general  size,  there  being  a  marked 
tendency  to  enlargement  of  peripheral  parts  under 
high  temperature,  or  toward  the  tropics, — hence  south- 
ward in  North  America.  This  is  more  readily  seen  in 
birds  than  in  mammals,  in  consequence,  mainly,  of 
their  peculiar  type  of  structure.  In  mammals  it  is 
manifested  occasionally  in  the  size  of  the  ears  and  feet, 
and  in  the  horns  of  bovines,  but  especially  and  more 
generally  in  the  pelage.  At  the  northward,  in  individ- 
uals of  the  same  species,  the  hairs  are  longer  and 
softer,  the  under  fur  more  abundant,  and  the  ears  and 
the  soles  of  the  feet  better  clothed.  This  is  not  only 
true  of  individuals  of  the  same  species,  but  of  northern 
species  collectively  as  compared  with  their  nearest 
southern  allies.  Southern  individuals  retain  perma- 
nently, in  many  cases,  the  sparsely  clothed  ears  and 
the  naked  soles  that  characterize  northern  individuals 
only  in  summer,  as  is  notably  the  case  among  the  dif- 
ferent squirrels  and  sphermophiles. 

"In  mammals  which  have  the  external  ear  largely 
developed — as  in  the  wolves,  foxes,  some  of  the  deer, 
and  especially  the  hares, — the  larger  size  of  this  organ 
in  southern  as  compared  with  northern  individuals  of 
the  same  species  is  often  strikingly  apparent.  It  is 
more  especially  marked,  however,  in  species  inhabit- 
ing extensive  open  plains  and  semi-desert  regions. 
The  little  wood  hare,  or  gray  rabbit  {Lfyus  sylvaticus), 
affords  a  case  in  point.  This  species  is  represented, 
in  some  of  its  varieties,  across  the  whole  breadth  of 
the  continent,  and  from  the  northern  border  of  the 
United  States  southward  to  Central  America,  but  in 


54     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

different  regions  by  geographical  races  or  subspecies. 
In  addition  to  certain  differences  of  color  and  general 
size,  the  ears  vary  still  more  strongly.  In  the  form 
inhabiting  tire  Great  Plains,  commonly  known  as  the 
little  sage-brush  hare  (Z.  sylvaticus  nuttalli},  the  ears 
are  considerably  longer  than  in  the  eastern  variety, 
and  increase  in  size  from  the  north  southward,  reach- 
ing their  greatest  development  in  Western  Arizona  and 
the  desert  region  further  westward  and  southward, 
where  the  variety  is  characterized  mainly  by  the  large 
size  of  its  ears,  which  are  in  this  race  nearly_twice  the 
size  they  attain  in  the  eastern  variety.  In  the  long- 
eared  ' jackass'  hares  of  the  plains,  the  ear  likewise 
increases  in  size  to  the  southward.  In  Lepus  callotis, 
for  example,  which  ranges  from  Wyoming  southward 
far  into  Mexico,  the  ear  is  about  one-fourth  to  one- 
third  larger  in  the  southern  examples  than  in  the  north- 
ern. The  little  brown  hare  of  the  Pacific  Coast  (Z. 
trowbridgei)  presents  a  similar  increase  in  the  size  of 
the  ear  southward,  as  does,  to  a  less  extent,  the  prairie 
hare  (Z.  eampestris).  Not  only  are  all  of  the  long- 
eared  species  of  American  hares  confined  to  the  open 
plains  of  the  arid  interior  of  the  continent,  but  over 
this  same  region  is  the  tendency  to  an  enlargement  of 
the  ear  southward  stronger  than  elsewhere.  It  is  also 
of  interest  in  this  connection  that  the  largest-eared 
hares  of  the  Old  World  occur  over  similar  open,  half- 
desert  regions,  as  do  also  the  largest-eared  foxes.  On 
our  western  plains,  the  deer  are  represented  by  a  large- 
eared  species.  Among  the  domestic  races  of  cattle, 
those  of  the  warm  temperate  and  intertropical  regions 
have  much  larger  and  longer  horns  than  those  of  north- 
ern countries  ;  as  is  shown  by  a  comparison  of  the 
Texan,  Mexican,  and  South  American  breeds,  with 


ON  VARIATION.  55 

the  northern  stock,  or  those  of  the  South  of  Europe 
with  the  more  northern  races.  In  the  wild  species  of 
the  Old  World,  the  southern  or  sub-tropical  are  re- 
markable for  the  large  size  of  their  horns.  The  horns 
of  the  American  prong-horn  {Antilocapra  americand}  are 
also  much  larger  at  southern  than  at  northern  locali- 
ties.1 Naturalists  have  also  recorded  the  existence  of 
larger  feet  in  many  of  the  smaller  North  American 
Mammalia  at  the  southward  than  at  the  northward, 
among  individuals  of  the  same  species,  especially 
among  the  wild  mice,  in  some  of  the  squirrels,  the 
opossum  and  raccoon,  as  well  as  in  other  species. 

"In  birds,  the  enlargement  of  peripheral  parts,  es- 
pecially of  the  bill,  claws,  and  tail,  is  far  more  obvious 
and  more  general  than  in  mammals.  The  bill  is  par- 
ticularly susceptible  to  variation  in  this  regard, — in 
many  instances  being  very  much  larger,  among  indi- 
viduals of  unquestionably  the  same  species,  at  the 
southward  than  at  the  northward.  This  accords  with 
the  general  fact  that  all  the  ornithic  types  in  which  the 
bill  is  remarkably  enlarged  occur  in  the  intertropical 
regions.  The  southward  enlargement  of  the  bill  within 
specific  groups  may  be  illustrated  by  reference  to  al- 
most any  group  of  North  American  birds,  or  to  those 
of  any  portion  of  the  continent.  As  in  other  features 
of  geographical  variation,  the  greatest  differences  in 
the  size  of  the  bill  are  met  with  among  species  having 
the  widest  distribution  in  latitude.  Among  the  species 
inhabiting  eastern  North  America  we  find  several  strik- 


IThe  deer  tribe,  in  which  the  antlers  increase  in  size  toward  the  north, 
offer  an  apparent  exception  to  the  rule  of  increase  in  size  of  peripheral  parts 
toward  the  tropics.  The  antlers  of  the  deer,  however,  are  merely  seasonal 
appendages,  being  annually  cast  and  renewed,  and  are  thus  entirely  different 
physiologically  from  the  horns  of  bovines,  which  retain  a  high  degree  of 
vitality  throughout  the  life  of  the  animal. 


56    PRIM 'A R  Y  FA  CTORS  OF  OR  CAN  1C  E  VOL  UTION. 

ing  examples  of  this  enlargement  among  the  sparrows, 
black-birds,  thrushes,  crows,  wrens,  and  warblers,  in 
the  quail,  the  meadow-lark,  the  golden-winged  wood- 
pecker, etc.  Generally  the  bill,  in  the  slender-billed 
forms,  becomes  longer,  more  attenuated,  and  more  de- 
curved  (in  individuals  specifically  the  same)  in  pass- 
ing from  the  New  England  States  southward  to  Flo- 
rida, while  in  those  which  have  a  short,  thick,  conical 
bill  there  is  a  general  increase  in  its  size  so  that  the 
southern  representatives  of  a  species,  as  a  rule,  have 
thicker  and  longer  bills  than  their  northern  relatives, 
though  the  birds  themselves  are  smaller.  There  is 
thus  not  only  generally  a  relative,  but  often  an  abso- 
lute, increase  in  the  size  of  the  bill  in  the  southern 
races.  The  species  of  the  Pacific  Coast  and  of  the  in- 
terior afford  similar  illustrations,  in  some  cases  more 
marked  even  than  in  any  of  the  eastern  species.  More 
rarely,  but  still  quite  frequently,  is  there  a  similar  in- 
crease in  the  size  of  the  feet  and  claws. 

"The  tail,  alsq,  affords  an  equally  striking  exam- 
ple of  the  enlargement  of  peripheral  parts  southward. 
Referring  again  to  the  birds  of  the  Atlantic  Coast, 
many  of  the  above-named  species  have  the  tail  abso- 
lutely longer  at  southern  localities  than  at  northern, 
and  quite  often  relatively  longer.  Thus  while  the  gen- 
eral size  decreases,  the  length  of  the  tail  is  wholly 
maintained,  or  decreases  less  than  the  general  size ; 
but,  in  some  cases,  while  the  general  size  is  one-tenth 
or  more  smaller  at  the  south,  the  tail  is  ten  to  fifteen 
per  cent,  longer  than  in  the  larger  northern  birds. 
Some  western  species  are  even  more  remarkable  in 
this  respect ;  and  in  consequence  mainly  of  this  fact 
the  southern  types  have  been  varietally  separated  from 
the  shorter-tailed  northern  forms  of  the  same  species. 


ON  VARIATION.  57 

"Variations  in  color  with  locality  are  still  more  ob- 
vious, particularly  among  birds,  in  which  the  colors 
are  more  positive,  the  contrasts  of  tints  greater,  and 
the  markings  consequently  better  denned  than  is  usu- 
ally the  case  in  mammals.  The  soft  finely-divided 
covering  of  the  latter  is  poorly  fitted  for  the  display 
of  the  delicate  pencilings  and  the  lustrous,  prismatic 
hues  that  so  often  characterize  birds.  Mammals,  how- 
ever, present  many  striking  instances  of  geographical 
variation  in  color. 

"As  already  stated,  geographical  variations  in  color 
may  be  conveniently  considered  under  two  heads. 
While  the  variation  with  latitude  consists  mainly  in  a 
nearly  uniform  increase  in  one  direction,  the  variation 
observed  in  passing  from  the  Atlantic  Coast  westward 
is  more  complex.  In  either  case,  however,  the  varia- 
tion results  primarily  from  nearly  the  same  causes, 
which  are  obviously  climatic,  and  depend  mainly  upoi 
the  relative  humidity,  or  the  hygrometric  conditions 
of  the  different  climatal  areas  of  the  continent.  In  re- 
spect to  the  first,  or  latitudinal  variation,  the  tendency 
is  always  toward  an  increase  in  intensity  of  coloration 
southward.  Not  only  do  the  primary  colors  become 
deepened  in  this  direction,  but  dusky  and  blackish 
tints  become  stronger  or  more  intense,  iridescent  hues 
become  more  lustrous,  and  dark  markings,  as  spots 
and  streaks  or  transverse  bars,  acquire  greater  area. 
Conversely,  white  or  light  markings  become  more  re- 
stricted. In  passing  westward  a  general  and  gradual 
blanching  of  the  colors  is  met  with  on  leaving  the 
wooded  regions  east  of  the  Mississippi,  the  loss  of 
color  increasing  with  the  increasing  aridity  of  the  cli- 
mate and  the  absence  of  forests,  the  greatest  pallor 
occurring  over  the  almost  rainless  and  semi-desert  re- 


58     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION, 

gions  of  the  Great  Basin  and  Colorado  Desert.  On 
the  Pacific  Slope,  north  of  California,  the  color  again 
increases,  with  a  tendency  to  heavy,  sombre  tints  over 
the  rainy,  heavily-wooded  region  of  the  Northwest 
Coast."1 


2.  VARIATION  IN   STRUCTURAL  CHARACTERS. 

Modifications  of  structural  characters  may  appear 
quite  independently  of  variation  of  specific  ones.  In- 
deed, generic  characters  have  at  times  changed 
completely  without  the  appearance  of  corresponding 
changes  in  the  more  superficial  characters  which  de- 
fine the  species.  Thus  changes  in  the  dentition  of 
some  of  the  Mammalia  appear  within  the  limits  of 
species,  which,  should  they  become  permanent,  would 
entitle  the  two  sets  of  individuals  which  display  the 
different  dentitions  to  be  placed  in  different  genera. 

Some  striking  examples  of  how  generic  characters 
may  undergo  metamorphosis  without  corresponding 
changes  in  specific  characters,  have  been  brought  to 
light  by  Dr.  William  H.  Dall  among  the  Brachiopo- 
dous  Mollusca.  Some  of  the  species  of  different  gen- 
era can  scarcely  be  distinguished,  except  by  compari- 
son of  their  generic  characters.  I  have  cited  the 
axolotls  as  illustrative  of  this  phenomenon.  Here  the 
same  species  may  reproduce  as  a  permanent  larva,  or 
as  an  adult.  Dume"ril  has  shown  that  the  North  Amer- 
ican salamander  (Amblystoma  tigrinuni}  can  lay  and 
fertilize  eggs  before  the  metamorphosis  is  passed.  I 
have  since  observed  that  the  females  of  the  allied  spe- 
cies of  Amblystomidae,  the  Chondrotus  tenebrosus  B.  and 
G.,  of  California  contain  mature  eggs  ready  for  de- 

1  The  Radical  Review,  May,  1877. 


ON  VARIATION.  59 

posit,  and  have  supposed  that  this  species  has  also  the 
same  power.1  The  difference  between  such  larvae  and 
the  adult  which  has  passed  the  metamorphosis  is  great. 
It  extends  not  merely  to  the  branchial  processes,  but 
to  the  splenial  teeth,  which  are  shed,  and  to  the  palato- 
pterygoid  arch,  which  is  absorbed,  and  to  the  pos- 
terior ceratobranchial  and  epibranchial  cartilages,  which 
are  absorbed.  In  the  larva  of  the  C.  tenebrosus  the 
palatopterygoid  arches  and  epibranchials  are  ossified, 
so  that  the  probability  of  its  being  able  to  maintain  an 
independent  existence  as  a  larva  is  greater  than  in  the 
case  of  the  A.  tigrinum.  In  this  type,  then,  each  spe- 
cies displays  variations  concomitant  with  reproductive 
maturity,  which  are  not  only  of  generic,  but  of  family 
significance.  In  a  third  species,  the  Siredon  mexica- 
num,  no  metamorphosis  has  yet  been  shown  to  take 
place,  so  that  it  is  probable  that  it  reproduces  ordina- 
rily while  in  the  branchiferous  stage.  Yet  it  is  only 
specifically  different  from  the  larva  of  the  Amblystoma 
tigrinum. 

Excellent  illustrations  of  the  serial  appearance  of 
generic  characters  may  be  seen  in  the  family  of  the 
dogs  (Canidae).  In  the  true  genus  Canis,  the  dental 
formula  is,  I.  |;  C.  \\  P.  m.  f ;  M.  f .  The  inferior  sec- 
torial  (m.  i)  has  a  metaconid,  and  the  second  inferior 
true  molar  has  two  roots.  It  not  unfrequently  hap- 
pens, however,  that  the  last  inferior  molar  (m.  3)  is 
wanting ;  and  in  some  cases  the  inferior  m.  2  has  but 
one  root.  When  in  addition  to  this,  as  in  some  of  the 
black-and-tans,  in  the  Mexican  naked  dog,  and  in  the 
pug,  the  inferior  m.  i  loses  its  metaconid,  we  have  the 
genus  Synagodus.  Occasionally  the  pug  dog,  and  fre- 
quently the  Mexican  dog,  loses  one  of  its  premolars 

IBatrachia  of  North  America,  1888,  p.  113,  PI.  xxii,  xxiii. 


60    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

from  both  jaws.  The  Japanese  spaniel  goes  still  fur- 
ther, and  usually  loses  also  its  second  superior  true 
molar  and  frequently  another  premolar  from  each  jaw; 
and  we  then  have  a  dentition  which  indicates  a  third 
genus,  which  has  been  called  Dysodus.  Its  dental 
formula  is  I.  $ ;  C.  \ ;  P.  m.  \-\ ;  m.  J.  Transitions 
between  this  and  the  normal  dentition  of  Canis,  in  all 
respects  can  be  found  in  the  smaller  domesticated 
dogs.  And  these  modifications  are  not  pathological, 
but  simply  express  a  rapid  metamorphosis  of  the  den- 
tition towards  the  reduced  formula  which  is  charac- 
teristic of  the  cats.  And  while  the  most  characteristic 
dentitions  belong  to  particular  species  (or  races)  of 
dogs,  many  of  the  single  modifications  are  both  absent 
and  present  in  dogs  of  the  same  species  or  race.  And 
these  are  the  kind  of  characters  which  are  observed 
to  mark  the  slow  progress  during  long  geologic 
ages,  of  mammals  of  various  other  groups.  These 
modifications  are  not  promiscuous,  but  are  in  the  di- 
rect line  of  change  which  has  characterized  all  Mam- 
malia during  geologic  time;  i.  e.,  the  reduction  of  the 
numbers  of  the  molar  teeth.  And  in  greater  detail, 
the  loss  of  metaconid  of  the  inferior  sectorial,  and  loss 
of  posterior  true  molars,  are  the  exact  losses  which  the 
carnivorous  type  has  undergone  in  the  evolution  of 
the  cats. 

A  significant  modification  of  the  third  superior  pre- 
molar has  been  observed  by  Dr.  Horace  Jayne  to  be 
occasionally  met  with  in  the  domestic  cat.  Sometimes 
an  internal  cusp  (deuterocone),  with  a  corresponding 
root  is  developed,  giving  rise  to  a  tritubercular  crown. 

Similar  observations  have  been  made  on  the  denti- 
tion of  man,  which  presents  two  phenomena  of  varia- 
tion of  opposite  phylogenetic  significance.  I  have 


ON  VARIATION.  61 

shown1  that  most  of  the  Indo-European  race,  together 
with  the  Esquimaux,  present  a  reversion  to  a  lemu- 
rine  form  in  the  second  and  third  superior  molars,  and 
sometimes,  in  the  case  of  the  Esquimaux,  in  the  first 
superior  molar  also.  I  have  also  shown,2  after  a  study 
of  the  dentition  of  the  extinct  Mammalia,  that  the  more 
complex  molars  of  later  placental  orders,  have  been 
derived  from  a  tritubercular  type,  which  prevailed 
throughout  the  earth  just  before  the  opening  of  the 
Eocene  period.  In  the  line  of  human  and  quadruma- 
nous  phylogeny,  the  lemurs  of  the  Eocene  period  pre- 
sented this  type  of  molar  in  the  upper  jaw,  and  mostly 
continue  to  do  so  to  the  present  time.  The  true  mon- 
keys, however,  added  the  fourth  tubercle  or  hypocone, 
in  accordance  with  the  developmental  law  in  Mamma- 
lia generally,  and  the  apes  and  men  of  the  lower  races 
present  the  same  characteristic.  Now,  in  the  yellow 
race  the  hypocone  of  the  last  molar  is  generally  want- 
ing, while  in  the  white  race  it  is  usual  to  find  it  absent 
from  both  the  second  and  third  molars.  In  this  we 
have  a  case  of  reversion. 

The  reduction  of  the  third  (last)  superior  molar, 
and  of  the  inferior  as  well,  has  gone  further  in  the 
white  race,  since  the  tooth  is  frequently  abnormally 
small,  abortive,  or  totally  wanting.  The  external  su- 
perior incisor  has  a  similar  history,  although  its  reduc- 
tion and  loss  is  not  nearly  so  frequent  as  that  of 
the  last  molars.  These  losses  from  the  dental  series 
are  not  of  the  nature  of  reversions,  since  the  number 
of  teeth  is  more  and  more  numerous  as  we  recede  in 
time  along  the  line  of  human  ancestry.  It  is,  on  the 
contrary,  the  continuation  of  a  process  which  has  been, 

1  American  Journal  of  Morphology ,  1888,  p.  7. 

2  American  Naturalist,  1884,  p.  350;  Origin  of  the  Fittest,  1887,  p.  347. 


62     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

as  already  remarked,  common  to  all  the  Mammalia,  of 
reduction  in  the  number  of  teeth.  Thus  men  with  fewer 
teeth  are  more  advanced  than  those  with  more  numer- 
ous ones ;  while  people  with  tritubercular  superior 
molars  have  reverted  to  an  ancient  type  ;  and  both  re- 
sults are  probably  attained  by  the  same  physiologic 
process,  i.  e.  defect  of  nutrition.  It  is  to  be  remem- 
bered also,  in  connection  with  our  argument,  that  these 
dental  variations  are  modifications  of  generic  charac- 
ters, and  that  they  are  in  definite  directions,  and  are 
not  promiscuous.  With  regard  to  the  question  as  to 
whether  dental  variations  in  man  are  promiscuous  or 
not,  we  have  better  opportunities  of  investigation  than 
in  the  case  of  the  lower  animals  generally.  It  may  be 
safely  asserted  that  the  dental  variations  above  cited 
are  by  far  the  most  frequent  in  man,  and  that  all  others 
put  together  are  relatively  insignificant. 

3.  SUCCESSIONAL  RELATION. 

As  the  biologic  types  are  variations  become  perma- 
nent, it  is  important  to  examine  how  the  former  stand 
related  to  each  other.  These  relations  express  the 
direction  which  variation  has  taken,  and  throw  a  great 
deal  of  light  on  the  nature  of  the  process.  That  exist- 
ing types  of  all  grades  are  the  result  of  the  isolation  of 
variations  of  species,  is  shown  by  the  frequent  exam- 
ples of  incomplete  isolation,  which  follows  inconstancy 
of  the  definitive  characters.  Groups  of  individuals 
which  display  this  partial  isolation  are  termed  sub- 
species. 

As  an  illustration  of  the  mingling  of  isolated  groups 
of  individuals  (species)  with  imperfectly  isolated  groups 
(subspecies),  in  a  single  genus,  I  refer  to  the  American 


ON  VARIATION.  63 

garter-snake  (genus  Eutaenia  B.  and  G.).  An  exami- 
nation of  several  hundred  individuals  of  this  genus 
yielded  the  following  results :  I  found  seventeen  groups 
of  individuals,  which  could  be  said  to  be  completely 
isolated  in  characters,  with  very  few  exceptions.  Eight 
other  groups  (species)  are  probably  isolated,  but  they 
are  not  represented  by  a  sufficiently  large  number  of 
specimens  to  yield  a  satisfactory  demonstration.  Of 
the  seventeen,  four  species  embrace  fifteen  non-isolated 
geographical  forms  (subspecies),  besides  the  typical 
forms  (eight  of  which  are  included  under  the  E.  sirta- 
lis);  and  two  others  include  three  color  forms  easily 
recognizable,  besides  the  typical  ones.  Similar  phe- 
nomena are  presented  in  every  part  of  the  animal  and 
vegetable  kingdoms. 

One  of  the  most  instructive  natural  divisions  for 
the  study  of  taxonomic  relations  as  the  result  of  varia- 
tion, on  account  of  the  simplicity  of  the  relations  pre- 
sented, is  the  Batrachia  Salientia,  or  the  order  of  Ba- 
trachia  to  which  belong  the  toads,  frogs,  etc.  Omitting 
the  very  restricted  suborders  of  the  Aglossa  and  Gas- 
trechmia,  the  Batrachia  Salientia  fall  into  two  divi- 
sions, which  differ  only  in  the  structure  of  the  lower 
portion  of  their  scapular  arch,  or  shoulder-girdle.  In 
the  one  the  opposite  halves  are  capable  of  movements 
which  contract  or  expand  the  capacity  of  the  thorax ; 
in  the  other  the  opposite  halves  abut  against  each 
other  so  as  to  be  incapable  of  movement,  thus  pre- 
serving the  size  of  the  thoracic  cavity.  But  during  the 
early  stages,  the  frogs  of  this  division  have  the  mova- 
ble shoulder-girdle  which  characterizes  those  of  the 
other  division,  the  consolidation  constituting  a  modifi- 
cation superadded  in  attaining  maturity.  Further- 
more, young  Salientia  are  toothless,  and  one  section  of 


64     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

the  species  with  embryonic  shoulder-girdle  never  ac- 
quire teeth.  The  suborder  with  embryonic  shoulder- 
girdle  is  called  the  Arcifera,  and  that  which  is  ad- 
vanced in  this  respect  is  the  Firmisternia.  Now  the 
frogs  of  each  of  these  divisions  present  nearly  similar 
scales  of  development  of  another  part  of  the  skeleton, 
viz.,  the  bones  of  the  top  of  the  skull.  We  find  some 
in  which  one  of  these  bones  (ethmoid)  is  represented 


Fig.  17- 


Fig.  16. 


SHOULDER-GIRDLES  OF  "ANURA." 

Fig.  15. — Of  the  Arciferous  type  (Phyllomedusa  bicolor}.  Fig.  16,  Rana 
temporaria,  tadpole  with  budding  limbs.  Fig.  17,  do.,  adult.  Figs.  16  and  17 
from  Parker. 

by  cartilage  only,  and  the  frontoparietals  and  nasals 
are  represented  by  only  a  narrow  strip  of  bone  each. 
In  the  next  type  the  ethmoid  is  ossified  ;  in  the  next, 
we  have  the  frontoparietal  completely  ossified,  and  the 
nasals  range  from  narrow  strips  to  complete  roofs ;  in 
the  fourth  station  on  the  line,  these  bones  are  rough, 
with  a  hyperostosis  of  their  surfaces  ;  and  in  the  next 
set  of  species  this  ossification  fills  the  skin,  which  is 
thus  no  longer  separable  from  the  cranial  bones  ;  in 


ON  VARIATION.  65 

the  sixth  form  the  ossification  is  extended  so  as  to  roof 
in  the  temporal  muscles  and  inclose  the  orbits  behind, 
while  in  the  rare  seventh  and  last  stage,  the  tympanum 
is  also  inclosed  behind  by  bone.  Now  all  of  these 
types  are  not  found  in  all  of  the  families  of  the  Salien- 
tia,  but  the  greater  number  of  them  are.  SMC  principal 
families,  four  of  which  belong  to  the  Arcifera,  are 
named  in  the  diagram  below,  and  three  or  four  others 
might  have  been  added.  I  do  not  give  the  names  of 
the  genera  which  are  defined  as  above  described,  re- 
ferring to  the  explanation  of  the  cuts  for  them,  but  in- 
dicate them  by  the  numbers  attached  in  the  plate, 
which  correspond  to  those  of  the  definitions  above 
given.  A  zero  mark  signifies  the  absence  or  non-dis- 
covery of  a  generic  type. 

Sternum  embryonic.    Arcifera.  Sternum  complete 


Toothless.  Toothed.  Firmisternia. 


Bufonidae.     Scaphiopidae.     Cystignathidae.     Hylidae.     Ranidae. 

1 10  I  I  O 

2 —  C  2  2  2  O 

3—30  333 

4—4  4  4  44 

5—5  5  °  55 

6—6  6  6  66 

7 —  70  o  o  o 

It  is  evident,  from  what  has  preceded,  that  a  per- 
fecting of  the  shoulder-girdle  in  any  of  the  species  of 
the  arciferous  columns  would  place  it  in  the  series  of 
Firmisternia.  An  accession  of  teeth  in  a  species  of  the 
division  BufonidceviQ>\A<\  make  it  one  of  the  Scaphiopid(z\ 
while  a  small  amount  of  change  in  the  ossification  of 
the  bones  of  the  skull  would  transfer  a  species  from 
one  to  another  of  the  generic  stations  represented  by 
the  numbers  of  the  columns  from  one  to  seven. 


Fig.  19- 

SCAPHIOPID-E  AND  PELOBATID.*. 


Fig.  20. 
HYLID.*. 


Fig.  21. 
CYSTIGNATHID.S. 


68    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

That  the  above  generic  divisions  have  been  actually 
developed  from  each  other  is  demonstrated  by  the  oc- 
currence of  occasional  intermediate  forms.  Thus  no 
generic  distinction  can  be  maintained  between  types 
third  and  fourth  in  the  family  of  toads  (Bufonidae),  so 
complete  is  the  transition  between  them.  In  Hylidae 
and  Cystignathidae  occasional  transitions  between  types 
second  and  third  occur.  In  the  Scaphiopidae  the  sub- 
species Spea  hammondii  intermontana  sometimes  has  the 
frontoparietal  fontanelle  open,  sometimes  closed.  I 
have  seen  some  adult  specimens  of  Rana  virescens  au- 
stricola  from  Central  America  with  the  ethmoid  bone 
unossified  above,  as  in  the  genus  Ranula.  The  rugose 
cranium  is  only  acquired  in  old  age  of  some  of  the  spe- 
cies of  Polypedates  of  India.  Yet  these  genera  are  as 

EXPLANATION  OF  CUTS  OF  CRANIA  OF  SALIENTIA. 

The  numbers  in  each  column  correspond  with  the  types  of  ossification 
mentioned  in  the  text,  and  are  the  same  as  those  in  the  table  of  families  given 
in  the  same  connection.  The  power  numbers  attached  to  No.  4,  represent  the 
degree  of  ossification  of  the  nasal  bone,  except  -l,  which  signifies  unossified 
ethmoid.  Most  of  the  cuts  are  original. 

Fig.  18. — BUFONIDAE. — No.  i,  anterior  part  of  skull  of  Chelydobatrachus 
gouldii  Gray,  from  Australia.  No.  4,  do.  of  Schismaderma  carens  Smith,  South 
Africa.  No.  5,  'top  of  head  of  Peltaphryne  peltacephala  D.  and  B.,  Cuba.  No. 
7,  top  of  head  of  Otaspis  empusa  Cope,  Cuba. 

Fig.  19.— SCAPHIOPID.E  AND  PELOBATiD^E.— No.  2,  diagram  of  top  of  cranium 
of  Didocus  calcaratus  Micahelles,  Spain.  No.  5,  skull  of  Scaphiopus  holbrookii 
Harl.,  United  States.  No.  6,  skull  of  Cultripes provincialis,  from  France,  after 
Duges. 

Fig.  20. — HYLID-E. — No.  I,  Thoropa  miliaris  Spix.,  Brazil.  No.  2,  Hypsi- 
boas  doumercii  D.  and  B.,  Surinam.  No.  al,  Hypsiboas punctatus  Schn.,  Brazil. 
No.  4^,  Scytopis  venulosus  Daudin,  Brazil.  No.  5,  Osteocephalus planiceps  Cope, 
E.  Peru.  No.  6,  Trachycephalus  geographicus  D.  and  B.,  after  Steindachner. 

Fig.  21. — CYSTIGNATHID.*. — No.  i,  Eusophus  nebulosus  Gir.,  Chili.  No.  2, 
Borborocoetes  tasmaniensis  Gthr.,  Tasmania.  No.  3,  Elosia  nasus  Licht.,  Bra- 
zil. No.  4,  Hylodes  oxyrhynchus  D.  and  B.,  West  Indies.  No.  6,  Calyptocepha- 
lus gayi  D.  and  B.,  Chili. 

Fig.  22. — RANID.E. — No.  4-  1,  Ranula  ckrysoprasina  Cope,  Costa  Rica.  No. 
4!,  Rana  clamata  Daud.,  N.  America.  No.  48,  Rana  agilis  Thomas,  Europe. 
No.  48,  Rana  hexadactyla  Less.,  India.  No.  5,  Polypedates  quadrilineatus  D. 
and  B.,  Ceylon. 


ON  VARIATION.  6g 

well  defined  as  closely  allied  genera  in  most  natural 
divisions. 

It  is  seldom  that  so  many  stages  of  developmental 
series  survive  so  as  to  be  contemporaries,  as  in  this 
case  of  the  Batrachia  Salientia.  In  order  to  obtain 
such  series  we  usually  have  to  explore  the  ages  of  the 
past.  In  the  higher  groups  this  is  also  the  case,  but 
here  we  have  also  occasional  examples  of  the  persis- 
tence of  fairly  complete  series.  Such  a  one  is  pre- 
sented by  the  suborder  Artiodactyla  of  the  Diplarth- 
rous  Ungulate  Mammalia.  I  give  the  definitions  of 
the  succession  of  the  existing  families. 

I.  Molars  bunodont  (tubercular) ;  superior  incisors  generally  pres- 
ent.    No  cannon  or  naviculocuboid  bones. 

Lateral  toes  well  developed  ;  Hippopotamida. 

Lateral  toes  rudimental ;  Suidtz. 

II.  Molars  selenodont  (crescent-bearing).  (Lateral  toes  rudimental 
or  wanting). 

A.  Premolars  with  one  row  of  lobes. 

No  naviculocuboid  bone  ;  one  superior  incisor  ;  a  can- 
non bone ;  Camelidce. 
A  naviculocuboid  bone ;  no  superior  incisor ;  (cannon 
bone  variable) ;                                               Tragulida. 
AA.  Premolars  with  two  rows  of  tubercles  ;  a  naviculocuboid 
and  cannon  bones  ;  no  incisors  above. 

Premolar  iii  with  only  one  row  of  lobes  ;  canine  teeth, 
no  horns ;  Moschida. 

Premolar  iii  with  two  rows  of  lobes ;  fixed  horns ;  no 
canines  above  ;  Bovida. 

Premolar  iii  with  two  rows  of  lobes ;  horns  decidu- 
ous ;  Cervidtz. 

In  this  suborder  we  see  a  gradual  complication  of 
the  structure  of  the  molar  teeth,  and  a  loss  of  the  in- 
cisors. In  the  limbs  we  observe  the  successive  loss  of 
the  lateral  digits,  and  the  fusion  of  elements, — as  the 
metapodials  into  cannon  bones,  and  the  elements  of 


7o    PRIMAR  Y  FA  CTORS  OF  OR GANIC  E  VOL  UTION. 

the  tarsus,  and,  what  is  not  stated  in  the  above  table, 
of  the  carpus  also.  Finally  there  is  the  remarkable 
development  of  horns  on  the  head.  When  we  come 
to  examine  the  phylogeny  of  this  order  we  will  find 
how  completely  these  characters  are  the  result  of  the 
fixation  of  variations  which  have  appeared  in  past  geo- 
logic ages,  and  how  various  are  the  combinations  and 
modifications  presented  by  the  extinct  types. 

Few  natural  groups  permit  of  representation  of 
their  subdivisions  in  linear  series.  The  only  correct 
representation  is  in  the  form  of  a  branching  tree,  and 
this  cannot  be  well  done  in  flat  projection  on  the  pages 
of  a  book.  Each  branch  taken  by  itself,  however, 
yields  itself  for  a  longer  or  shorter  space  to  linear 
treatment. 

For  an  example  of  such  linear  series  in  higher 
groups  I  turn  again  to  the  Batrachia  Salientia.  Here 
the  two  suborders  of  the  Arcifera  and  Firmisternia  pre- 
sent the  following  interesting  parallels  : 

ARCIFERA.  FIRMISTERNIA 

I.   Without  teeth. 
a.  With  sacral  diapophyses  dilated. 

Brevicipitidae. 
Bufonidae J  Engystomidse. 

[  Phryniscidae. 
aa.  Sacral  diapophyses  cylindric. 

Dendrophryniscidae.    Dendrobatidae 

II.   With  premaxillary  and  maxillary  teeth  only. 
a.    With  sacral  diapophyses  dilated. 

Pelod>"i<te  I  f  Dyscophid*. 

Suf) 153? 

aa.  With  sacral  diapophyses  cylindric. 

Cystignathidae...  .    f  Colostethidae. 

I  Ranidae. 


ON  VARIATION.  71 

III.  Teeth  in  both  jaws. 
a.  Sacral  diapophyses  not  dilated. 

Amphignathodontidae  \  Ceratobatrachidse. 

Hemiphractidae J 

In  strict  reference  to  the  structure  of  the  hind  feet 
the  following  parallels  may  be  drawn : 

FlRMISTERNIA.  RANID^.  ARCIFERA. 

External  rnetatarsal  free  : 

Aquatic.  Rana.  Pseudis. 

Subfossorial.  Hoplobatrachus.  Mixophyes. 
External  rnetatarsal  attached : 
Feet  webbed — 

Burrowing.  Pyxicephalus.  Ceratophrys. 

Arboreal  (vom.  teeth).  Leptopelis.  Hyla. 

Arboreal  (no  v.  teeth).  Hyperolius.  Hylella. 

Aquatic.  Heteroglossa.  Acris. 
Feet  not  webbed — 

Terrestrial.  Cassina.  Cystignathus. 

Terrestrial,  spurred.  Hemimantis.  Paludicola. 

Parallel  series  like  those  of  the  Arcifera  and  Fir- 
misternia  I  have  termed  " homologous,"  and  the  cor- 
responding terms  of  such  series  I  have  called  "  hete- 
rologous."1  Such  corresponding  phylogenetic  series 
are  homologous  to  each  other,  while  their  terms  or 
genera  are  heterologous  in  their  relation  to  correspond- 
ing terms  of  other  phyla.  In  such  cases  the  genera  or 
terms  of  a  series  owe  their  resemblances  to  each  other 
to  inheritance;  but  they  owe  their  resemblances  to 
their  corresponding  or  heterologous  genera,  to  identi- 
cal evolutionary  influences.  Subsequently  to  my  pro- 
posal to  use  the  above  terms,  Prof.  E.  R.  Lankester 
proposed  the  word  "homogenous"  to  express  what  is 
conveyed  by  my  term  homologous,  and  "homoplastic" 
to  express  the  sense  of  heterologous.  For  the  two  con- 

1" Origin  of  Genera,"  Proceedings  Philadelphia  Acaderyy,  1868,  p.  281. 


72     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


ditions  he  coined  the  words  "homogeny  "  and  "ho- 
moplassy. "  The  terms  introduced  by  Lankester  differ 
from  mine  in  that  they  convey  implications  as  to  the 
origin  of  the  respective  conditions. 


3  4 

Fig.  23. — Feet  of  (1-2)  Uma  scoparia  Cope,  from  near  Tucson,  Arizona, 
and  (2-3)  Ptenopus garrulus  Smith,  from  South  Africa.  No.  i,  manus;  No.  2, 
pes;  Nos.  3-4,  pes.  Nos.  1-2,  original;  Nos.  3-4,  from  Boulenger. 

An  illustration  of  homoplassy  is  to  be  seen  in  the 
spines  on  the  head,  tail,  and  feet  of  lizards  which  in- 
habit desert  regions.  The  parallelism  between  Phry- 
nosoma  of  the  American  dry  regions,  and  the  Moloch 
of  the  corresponding  climates  of  Australia  has  been 


ON  VARIATION.  73 

already  noted.  In  the  deserts  of  Asia,  South  Africa, 
and  North  America  some  of  the  lizards  exhibit  a  great 
elongation  of  the  lateral  scales  of  the  digits  on  one  or 
both  extremities.  These  become  fringes  of  spines, 
freely  articulated  at  their  bases  with  the  integument. 
By  penetrating  the  sand,  they  increase  the  hold  on  its 
yielding  surface,  and  greatly  improve  the  speed  of 
their  movements.  The  genera  in  which  this  structure 
is  conspicuous  in  the  three  localities  in  question,  be- 
long to  as  many  distinct  families.  Thus  in  Asia  it  is 
the  genus  Phrynocephalus  of  the  family  Agamidae ;  in 
South  Africa  it  is  Ptenopus  of  the  Gecconidae  ;  while 
in  North  America  it  is  Uma  of  the  Iguanidae.  I  give 
figures  of  the  feet  of  Ptenopus  and  Uma  for  comparison. 
(Fig.  23.)  Phrynocephalus  is  more  like  Uma  than  is 
Ptenopus. 

In  the  succeeding  chapters  of  this  book  many  illus- 
trations of  the  serial  relation  of  characters  will  be 
given,  so  that  it  is  not  necessary  to  occupy  more  space 
with  the  subject  here. 


CHAPTER  II.— PHYLOGENY. 


i.  GENERAL  PHYLOGENY. 

THE  actual  phylogeny  or  genealogy  of  organisms 
can  only  be  positively  determined  by  paleonto- 
logic  research.  We  have  been  able  in  this  way  to  ob- 
tain numerous  lines  of  descent  of  animals  and  some 
general  results  as  to  the  genealogic  relations  of  the 
primary  types  of  animals  and  plants.  Many  forms  of 
both  animals  and  plants  are  and  have  been  without 
those  hard  parts  which  are  susceptible  of  preservation 
in  the  formations  of  the  earth's  crust,  so  that  no  trace 
of  their  existence  remains  to  us.  In  these  cases  our 
resort  is  embryologic  investigation,  since  the  embry- 
onic history  is  a  more  or  less  complete  recapitulation 
of  the  types  of  the  past  ages,  from  which  the  existing 
ones  are  descended.  But  since  many  representatives 
of  the  ancient  and  primitive  forms  of  life  still  remain 
on  the  earth,  we  can  trace,  by  the  study  of  their  struc- 
ture, the  larger  features  of  general  phylogeny.  So  far 
as  we  have  compared  the  results  derived  from  these 
three  lines,  it  has  been  found  that  they  coincide  in 
their  indications.  We  have  in  this  a  satisfactory  proof 
that  our  conclusions  are  trustworthy  contributions  to 
the  knowledge  of  the  history  of  life. 

The  study  of  phylogeny  shows  that  the  evolution 


PHYLOGENY.  75 

of  life- forms  has  been  from  the  simple  to  the  complex, 
and  from  the  generalized  to  the  specialized.  These 
two  forms  of  expression  are  not  identical.  In  the 
phrase,  "from  the  simple  to  the  complex,"  is  implied 
an  ascending  scale  of  evolution.  In  the  phrase,  "  from 
the  generalized  to  the  specialized,"  we  may  include 
both  progressive  and  retrogressive  evolution.  Retro- 
gressive or  degenerative  evolution  has  been  a  frequent 
phenomenon  in  the  past,  and  scarcely  an  organism  ex- 
ists which  does  not  display  degeneracy  in  some  detail  of 
its  structure.  Progressive  evolution  has,  however,  not 
been  prevented  by  the  frequent  occurrence  of  an  op- 
posite process ;  and,  indeed,  degeneracy  of  parts,  or  of 
types  of  life,  have  been  necessary  to  the  advance  of 
other  and  better  organs  or  forms. 

It  is  necessary  to  an  understanding  of  the  laws  of 
evolution  to  get  beforehand  some  idea  of  what  that 
evolution  has  actually  been.  I  will,  therefore,  give  a 
general  outline  of  the  phylogeny  of  plants  and  animals, 
and  will  thus  illustrate  the  subject  in  full  detail  in  the 
case  of  the  Vertebrata,  where  our  facilities  are  espe- 
cially good. 

It  is  well  known  that  the  Protophyta  and  the  Pro- 
tozoa are  not  distinguishable  by  any  sharp  line  of  de- 
marcation. Chlorophyll,  which  is  so  characteristic  of 
plants,  is  absent  from  many  of  the  lowest  forms,  in- 
cluding the  entire  class  of  Fungi,  while  it  is  present 
in  a  few  of  the  lowest  animals.  The  capacity  for  mo- 
tion from  place  to  place,  so  general  in  animals,  at 
least  in  their  earlier  stages,  is  present  in  the  earlier 
stages  of  some  of  the  Algae,  and  is  universal,  except  at 
the  period  of  reproduction,  in  the  Myxomycetes.  If  it 
be  denied  that  the  latter  are  plants,  then  they  are  ani- 
mals which  do  not  reproduce  by  the  ordinary  process 


76    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

of  fission,  but  by  spores,  which  are  borne  together  in 
a  mass,  or  in  a  sporangium  distinguished  from  the  rest 
of  the  body.  A  distinction  between  the  lower  animals 
and  plants  is  that  the  former  introduce  their  food  at  a 
definite,  though  it  may  be  a  variable,  point  of  the  body; 
while  plants  absorb  their  nutriment  in  solution  at  all 
points.  It  is  however  demonstrated  that  some  animals 
(many  parasites)  nourish  themselves  in  the  same  man- 
ner as  do  plants ;  and  in  their  early  stages  the  Myxo- 
mycetes  have  the  feeding  habit  of  the  lowest  animals 
(Amoebae).  Both  animals  and  plants  from  a  morpho- 
logical point  of  view  have  a  common  origin,  in  a  nucle- 
ated, undivided,  more  or  less  globular  piece  of  proto- 
plasm or  sarcode. 

From  freely  moving  Protophyta  of"  this  form,  the 
vegetable  kingdom  took  its  rise.  They  first  of  all  as- 
sumed a  sessile  position  on  the  earth,  and  became 
what  one  may  call  earth-parasites.  This  abandonment 
of  free  mobility  we  cannot  hesitate  to  regard  as  the 
efficient  cause  of  a  degenerate  line  of  evolution.  There 
can  be  no  doubt  about  this,  since  fixity  of  habitat  at  once 
limits  enormously  the  range  of  active  influences  which 
tend  to  modify  an  organism,  whether  they  proceed 
from  within  it  or  from  without  it.  The  subsequent 
inclosure  of  the  protoplasm  in  a  structure  of  cellulose 
removes  them  from  many  of  the  stimuli  which  have  so 
potent  an  influence  in  the  life-history  of  animals,  and 
the  storage  of  other  substances,  as  proteids,  gums, 
resins,  etc.,  in  their  cells,  still  further  emphasizes  the 
distinction. 

From  this  beginning,  progress  in  plants  is  seen 
chiefly  in  the  modifications  of  their  methods  of  repro- 
duction. This  function  is  the  aim  of  the  vegetable 
kingdom  so  far  as  their  own  condition  is  concerned. 


PHYLOGENY.  77 

Incidentally  they  are,  however,  essential  to  the  exist- 
ence of  the  animal  kingdom,  since  they  alone  elaborate 
protoplasm  and  proteids  from  inorganic  nature.  In 
the  simplest  plants  there  is  no  sexuality,  and  repro- 
duction is  effected  by  spores  which  are  mere  fragments 
of  the  parental  protoplasm  (Protophyta).  In  the  next 
stage  sexual  conjugation  is  necessary,  but  the  sexes 
do  not  differ  from  each  other  in  characters  (Zygo- 
phyta).  In  the  third  stage  (Oophyta)  the  sexes  are 
distinct,  and  the  reproductive  elements  are  distin- 
guished as  female  germ-cell  and  male  antheridium. 
In  the  remaining  types  of  plants  a  distinct  set  of  indi- 
viduals, the  prothallia,  is  produced  by  cell-division, 
whose  function  is  sexual  reproduction,  thus  constitut- 
ing an  alternation  of  generations.  These  plants  may 
be  entirely  cellular  (Carpophyta),  or  may  be  furnished 
with  vascular  canals.  Of  the  latter  the  male  and  fe- 
male prothallia  may  be  naked  and  free  (Pteridophyta 
or  ferns,  etc.),  or  may  be  enclosed  in  modified  leaves, 
or  flowers,  the  Phaenogamia  or  flowering  plants. 

For  the  reasons  already  mentioned  the  order  of 
"  successional  relation  "  above  pointed  out,  is  likely  to 
prove  to  be  the  order  of  appearance  of  plants  in  time, 
and  that  such  is  the  fact  is  demonstrated  by  their  pa- 
leontology. In  the  earliest  beds  in  which  plants  are 
positively  known  to  occur,  the  Ordovician,  we  have 
only  Algae  (Zygophyta  and  Oophyta).  In  the  Siluric 
we  have  a  great  predominance  of  the  same  classes,  a 
very  few  species  of  which  appear  to  have  formed  great 
erect  stems.  In  the  next  period,  the  Devonic,  prob- 
able Carpophyta  are  present,  while  the  vascular  Pte- 
ridophyta appear  for  the  first  time,  and  in  consider- 
able numbers.  A  few  members  of  the  gymnospermous 
Phaenogamia  (Coniferae)  appear.  In  the  Carbonic  pe- 


78    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


3  CU  C  <  JL 

I  I  *   I  I 


O 


3    "S3 


PHYLOGENY.  79 

riod,  the  greatest  known  development  of  the  Pterido- 
phyta  (Lycopodia,  ferns,  Equiseta)  took  place,  while 
the  Gymnosperms  were  still  represented  by  a  few  gen- 
era. Their  period  of  development  or  acme  arrived  in 
the  Mesozoic  ages,  and  the  Pteridophyta  underwent  a 
corresponding  reduction  of  numbers  and  importance. 
Not  until  the  upper  Cretaceous  epoch  did  the  Angio- 
spermous  Phanerogams  with  their  attractive  flowers 
appear,  and  from  that  period  to  the  present  they  have 
gained  and  maintained  the  ascendency.  In  accord- 
ance with  the  mode  of  origin  of  tubular  flowers  by  the 
fusion  of  the  separate  petals  of  polypetalous  forms, 
we  find  that  the  former  succeeded  the  latter  in  time. 

We  may  review  this  brief  sketch  of  the  paleontol- 
ogy of  plants  in  the  preceding  phylogenetic  table.  " 

Turning  now  to  the  animal  kingdom,  its  order  of 
succession  may  also  be  perceived  in  existing  species. 
As  with  plants  we  commence  with  unicellular  asexual 
forms  (Protozoa).  Some  of  these  increase  by  division 
only  (Rhizopoda),  while  others  must  occasionally  con- 
jugate, since,  according  to  Maupas,  the  reproductive 
energy  is  exhausted  by  continued  self-division  (Infuso- 
ria). Such  structural  specializations  as  the  highest  of 
the  Protozoa  possess,  are  merely  vacuities  or  processes 
of  their  material,  for  the  purpose  of  internal  or  exter- 
nal motion.  In  the  second  grade  of  organization  ani- 
mals are  multicellular,  or  composed  oi  more  than  one 
protoplasmic  unit.  The  simplest  of  these,  as  Volvox, 
contains  no  specialized  organs,  but  seems  like  a  colony 
of  Protozoa,  although  all  its  cells  are  not  exactly  alike 
(Ryder).  An  appreciable  advance  of  structure  de- 
fines the  next  class,  the  Coelenterata.  Here  the  mul- 
ticellular mass  contains  a  distinct  digestive  chamber, 
from  which  usually  radiate  tubes  towards  the  periph- 


8o     PRIMAR  Y  FA CTORS  OF  ORGANIC  E VOL  UTION. 

ery,  which  distribute  the  products  of  digestion.  The 
first  nervous  threads  appear.  But  there  is  as  yet  no 
body  cavity  which  should  form  a  sac  in  which  the  or- 
gans of  nutrition  and  reproduction  should  be  sus- 
pended. The  Porifera  (sponges)  appear  to  be  a  much 
modified  form  of  this  type. 

This  grade  of  specialization  belongs  to  the  greater 
number  of  the  five  succeeding  classes,  the  Echinoder- 
mata,  Vermes,  Mollusca,  Arthropoda,  and  Vertebrata. 
Where  it  is  absent  from  a  few  of  the  three  lower 
classes,  it  is  supposed  to  have  disappeared  by  degen- 
eracy. The  Echinodermata  come  first  in  considera- 
tion. In  these  animals  the  form  inclines  to  be  radiated 
and  the  nervous  system  presents  no  single  axis,  but 
consists  of  branches  which  radiate  from  a  ring  sur- 
rounding the  oral  extremity  of  the  digestive  canal.  In 
the  second  type,  the  general  form  is  longitudinal  and 
may  be  segmented,  and  a  nervous  axis  may  extend 
longitudinally  from  one  or  more  points  on  the  ceso- 
phageal  ring.  These  are  the  Vermes  (true  worms). 
Embryology  indicates  clearly  the  common  origin  of 
the  Echinodermata  and  the  Vermes.  No  line  of  de- 
scent can  be  traced  from  the  former,  but  from  the  lat- 
ter we  have  traced  the  remaining  branches  of  animals, 
three  in  number.  Lowest  of  these  is  the  Mollusca. 
The  form  of  the  body  is  sac-like,  and  the  nervous  sys- 
tem displays,  typically,  besides  the  oesophageal  ring, 
a  second  ring,  consisting  of  lateral  commissures,  mak- 
ing a  single  median  ganglion  of  the  foot.  The  body 
is  not  segmented,  and  there  are  no  jointed  limbs.  In 
the  second  branch,  that  of  the  Arthropoda,  the  body 
is  longitudinal  and  segmented,  and  segmented  limbs 
are  present.  There  is  a  median  nervous  axis,  proceed- 
ing from  the  oesophageal  ring  along  the  inferior  axis 


PHYLOGENY.  81 

of  the  body,  connecting  several  ganglia,  (with  some 
exceptions  where  the  ganglia  are  fused  or  wanting). 
There  is  no  internal  skeleton.  In  the  last  and  highest 
branch,  that  of  the  Vertebrata,  the  body  is  longitudi- 
nal and  is  segmented.  It  has  a  longitudinal  nervous 
axis  on  the  superior  middle  line,  which  is  supported 
below  by  an  axis  of  resistant  material,  usually  bone, 
which  forms  the  axis  of  an  internal  skeleton.  Seg- 
mented limbs  are  present. 

The  lines  of  descent  of  these  branches  indicated  by 
embryology  are  as  follows  : 

Vertebrata. 
Arthropoda. 
Molh 


Mollusca. 
EchinodermatcL^ — -^^^^ 

Porifera. 

Coelenterata. 

Catallacta. 


Protozoa. 

The  above  series  present  a  history  which  is,  on  the 
whole,  very  different  from  that  already  described  as 
characterizing  the  vegetable  kingdom.  Between  the 
first  and  last  terms  of  the  series,  there  is  exhibited  a 
great  progressive  advance  in  all  the  higher  features  of 
life.  These  are  mobility,  and  such  control  over  the 
environment  as  it  gives ;  and  sensibility,  through  the 
development  of  a  nervous  system,  which  gives  control 
over  the  movements.  The  highest  development  is 
that  of  mental  characteristics,  as  emotions  and  intelli- 
gence, which  are  especially  seen  in  the  higher  Verte- 
brata. 


82     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

This  progress  has  not  been  accomplished  without 
much  degeneracy  by  the  way.  All  of  the  branches 
display  divisions  which  have  become  sessile,  and  some 
of  them  are  almost  altogether  so.  Among  Ccelenterata 
the  Actinozoa  are  fixed,  and  often  develop  a  calcareous 
skeleton.  Many  of  the  Hydroids  are  sessile.  The 
great  branch  of  the  Echinodermata  has  its  locomotive 
powers  greatly  curtailed,  and  many  of  them  are  per- 
manently sessile.  The  same  is  true  of  the  Mollusca. 
Both  divisions  are  at  one  side  of  the  line  of  progres- 
sive evolution  as  a  consequence  of  this  tendency.  The 
Vermes  display  in  their  free  representatives  the  condi- 
tions of  progressive  evolution.  Being  longitudinal 
and  bilateral,  one  extremity  becomes  differentiated  by 
first  contact  with  the  environment,  as  the  seat  of  spe- 
cial senses,  the  basis  having  been  secured  by  the  loca- 
tion there  of  the  nervous  centers  and  ring.  The  Ar- 
thropoda  present  us  with  a  great  development  of 
locomotive  organs,  and  of  special  senses.  As  a  whole, 
they  have  not  made  a  considerable  advance  into  the 
possession  of  the  higher  animal  mental  capacities,  but 
display  various  degeneracies  or  degenerate  tendencies 
among  themselves.  The  moderately  specialized  as  to 
structure  are  the  most  intelligent.  These  are  the  Hy- 
menoptera,  which  display  mental  capacity  superior  to 
that  of  many  Vertebrata.  The  latter  branch,  although 
presenting  one  sessile  type,  the  Urochorda,  has  pro- 
duced in  its  highest  class,  the  Mammalia,  the  most  gen- 
eral elevation  in  this,  the  highest  of  animal  functions. 
This  intelligence  is  in  most  of  the  types  expended  in 
preserving  themselves  from  destruction  against  hostile 
environments,  and  the  conquest  of  nature  thus  effected 
is  remarkable  from  a  physical  point  of  view,  but  is  an 
end  of  no  great  elevation  of  purpose  from  a  mental 


PHYLOGENY.  83 

standpoint.  It  is  only  in  the  most  intelligent  of  the 
Mammalia,  and  in  man,  that  we  behold  social  and  in- 
tellectual qualities  which  express  something  more  than 
a  mere  routine  of  material  existence. 

Since  Protozoa  are  very  fragile,  even  when  pos- 
sessed of  shells  of  mineral  salts,  we  cannot  expect  to 
discover  the  actual  date  of  their  first  appearance  on 
the  earth.  Nevertheless  they  have  "been  recently  dis- 
covered in  the  later  Archaean  (=Huronian)  beds  of 
France.  Some  of  the  simplest  Ccelenterata,  however, 
(the  Actinozoa),  have  deposited  lime  salts  in  the  septa 
of  their  digestive  chambers,  and  in  some  instances  over 
their  entire  surface,  so  that  their  preservation  has  been 
assured.  Thus  we  can  prove  that  the  simplest  coral 
animals  appear  in  the  oldest  rocks  of  sedimentary  ori- 
gin, the  Cambric.  Probably  Vermes,  and  positively 
Echinodermata,  Mollusca,  and  Arthropoda  (Trilobita), 
also  appear  in  the  Cambric.  Vertebrata  appear  defi- 
nitely in  the  Siluric  ;  their  supposed  appearance  in  the 
Ordovicic  being  very  doubtful. 

The  paleontologic  history  conforms  to  the  syste- 
matic order  in  so  far  as  it  shows  that  the  Ccelenterata 
appeared  first,  and  the  Vertebrata  last,  in  time.  A 
more  complete  correspondence  between  the  two  his- 
tories is  found  in  the  divisions  of  these  branches,  and 
I  will  take  up  the  Vertebrata  as  the  one  of  whose  be- 
ginning we  know  the  most,  and  are  likely  to  know 
more. 

2.  THE  PHYLOGENY  OF  THE  VERTEBRATA. 

a.   Phylogeny  of  the  Classes. 

As  the  illustrations  of  evolution  in  the  present  work 
are  mainly  drawn  from  the  Vertebrata,  I  go  somewhat 
into  detail  in  discussing  the  phylogeny  of  that  branch. 


84    PRIMAKS  FACTORS  OF  ORGANIC  EVOLUTION. 

They  present  the  advantage,  that,  since  they  appeared 
last  of  the  animal  kingdom  in  time,  we  can  obtain  a 
clearer  view  of  their  beginnings  than  in  the  case  of  the 
other  great  branches. 

Before  going  into  the  subject  I  wish  to  call  atten- 
tion to  a  prevalent  source  of  error  in  the  construction 
of  phylogenies.  This  is  the  confusion  of  ideas  general 
among  naturalists  who  are  not  at  the  same  time  com- 
petent systematists,  as  to  the  subordination  of  charac- 
ters. All  correct  phylogenetic  inference  depends  on  a 
correct  appreciation  of  the  value  of  characters.  Fail- 
ing this,  error  and  confusion  result.  If,  for  instance, 
it  is  alleged  that  such  a  genus  is  ancestral  to  another 
genus,  it  is  often  forgotten  that  the  descent  of  generic 
character,  and  not  specific  character,  is  meant.  The 
usual  type  of  critic  attempts  to  contradict  such  hy- 
pothesis by  showing  some  incongruity  in  specific  char- 
acters, a  matter  which  is  quite  irrelevant  to  the  issue. 
Thus  Madame  Pavlov  finds  that  Hippotherium  mediter- 
raneum  is  not  the  ancestor  of  Equus  caballus,  and  comes 
promptly  to  the  conclusion  that  the  genus  Hippothe- 
rium is  not  ancestral  to  the  genus  Equus.  This  is  a 
non  sequitur,  for  there  are  perhaps  twenty  species  of 
Hippotherium,  some  of  which  are  almost  certain  to 
have  been  ancestral  to  species  of  American  Equus.  In 
like  manner,  if  it  is  alleged  that  the  condylarthrous 
Mammalia  are  ancestral  to  the  Diplarthra,  if  it  should 
happen  that  no  known  genus  of  the  former  fits  exactly 
the  position  of  ancestor  to  any  genus  of  the  latter,  in 
our  present  state  of  knowledge,  the  contention  is  not 
thereby  vitiated,  and  it  is  implied  that  such  genus  will 
certainly  be  found.  If  it  is  also  alleged  that  Condy- 
larthra  have  been  the  ancestors  of  the  anthropoid  line, 
if  some  of  the  known  genera  of  the  former  turn  out  to 


PHYLOGENY.  85 

have  no  clavicle,  a  bone  which  is  possessed  by  the 
latter,  it  is  only  to  be  concluded  that  the  early  lemur- 
oids  were  derived  from  Condylarthra  which  possessed 
a  clavicle.  And  in  the  discussion  of  the  descent  of 
one  order  from  another,  care  must  be  taken  that  fam- 
ily, generic,  and  even  specific  characters  are  not  im- 
ported into  the  discussion. 

It  is  this  confusion  of  ideas  on  the  part  of  both 
phylogenists  and  their  critics,  that  has  brought  phylo- 
genetic  schemes  into  a  discredit  in  some  quarters, 
which  is  sometimes  deserved  and  sometimes  unde- 
served. Embryologists  are  especially  apt  to  construct 
impossible  phylogenies,  as  they  are  generally  not  sys- 
tematists,  and  frequently  not  anatomists.  An  excel- 
lent illustration  of  an  impossible  phylogeny  is  that  of 
the  fishes  published  a  few  years  ago  by  the  embryolo- 
gist  Dr.  Beard.  As  an  illustration  of  clean-cut  phy- 
logeny without  confusion,  I  cite  that  of  Haeckel ;  which 
I  have  shown  to  be,  as  regards  the  Vertebrata,  mainly 
correct. 

In  attempting  to  ascertain  the  course  of  evolution 
of  the  Vertebrata,  and  to  construct  phylogenetic  dia- 
grams which  shall  express  this  history,  among  the  dif- 
ficulties arising  from  deficient  information  one  is  espe- 
cially prominent.  As  is  well  known,  there  are  many 
types  in  all  the  orders  of  the  Vertebrata  which  present 
us  with  rudimentary  organs,  as  rudimental  digits,  feet 
or  limbs,  rudimental  fins,  teeth,  and  wings.  There  is 
scarcely  an  organ  or  part  which  is  not  somewhere  in  a 
rudimental  and  more  or  less  useless  condition.  The 
difficulty  which  these  cases  present  is,  simply,  whether 
they  be  persistent  primitive  conditions,  to  be  regarded 
as  ancestral  types  which  have  survived  to  the  present 
time,  or  whether,  on  the  other  hand,  they  be  results  of 


86     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

a  process  of  degeneration,  and  therefore  of  compara- 
tively modern  origin.  The  question,  in  brief,  is, 
whether  these  creatures  presenting  these  features  be 
primitive  ancestors  or  degenerate  descendants. 

A  great  deal  of  light  has  been  happily  thrown  on 
this  question,  as  regards  the  Vertebrata,  by  the  recent 
work  done  in  North  American  paleontology.  The  lines 
of  descent  of  many  of  the  minor  groups  have  been 
positively  determined,  and  the  phylogenetic  connec- 
tions of  most  of  the  primary  divisions  or  classes  have 
been  made  out.  The  result  of  these  investigations  has 
been  to  prove  that  the  evolution  of  the  Vertebrata  has 
proceeded  not  only  on  lines  of  acceleration,  but  also 
on  lines  of  retardation.  That  is,  that  evolution  has 
been  not  only  progressive,  but  at  times  retrogressive. 

The  Amphioxus  (genus  Branchiostoma)  is  generally 
regarded  as  the  ancestral  vertebrate.  There  are  many 
reasons  why  this  position  must  be  accepted,  although 
it  possesses  a  few  secondary  modifications.  Whether 
Branchiostoma  derived  its  descent  from  an  annelid 
worm,  or  from  a  tunicate,  is  a  vexed  question.  Brooks1 
remarks  as  to  this,  "Up  to  this  point  I  believe  that 
the  ancestral  history  of  the  tunicates  was  identical  with 
that  of  the  vertebrates ;  for  the  hepatic  coecum,  the 
dilated  pharynx,  the  pharyngeal  clefts,  the  hypophar- 
yngeal  gland,  and  the  peripharyngeal  bands,  have  been 
inherited  by  all  the  Chordata  (Vertebrata),  and  have 
impressed  themselves  so  firmly  in  their  organization 
that  even  the  highest  vertebrates  still  retain  them, 
either  as  vestiges  or  as  organs  which  have  been  fitted 
to  new  functions.  I  believe,  however,  that  while  they 
were  acquired  before  the  tunicates  diverged  from  the 
chordate  (vertebrate)  stem,  they  were  acquired  by  an 

1  Studies  from  the  Laboratory  of  the  Johns  Hopkins  University,  1893,  p.  175. 


PHYLOGENY.  87 

organism  whose  environment  and  habits  of  life  were 
essentially  like  those  of  the  modern  Appendicularia.' 
Appendicularia  is  well  known  as  the  tunicate  which 
retains  throughout  life,  the  notochord  and  tail  which 
characterize  the  larvae  of  other  Tunicata. 

Omitting  from  consideration  the  two  classes  above 
mentioned  (Acrania  and  Tunicata),  whose  remains 
have  not  yet  been  certainly  found  in  a  fossil  state,  there 
remain  the  following  :  the  Pisces,  Batrachia,  Mono- 
condylia,  and  Mammalia.1 

I  have  traced  the  origin2  of  the  Mammalia  to  the 
theromorous  reptiles  of  the  Permian  epoch,  and  these 
to  the  Cotylosauria.  The  latter  include  the  Pelycosau- 
ria,  Procolophonina,  Anomodontia,  and  perhaps  other 
orders.  In  the  Cotylosauria  the  temporal  region  is 
roofed  over,  which  roof  is  reduced  in  the  Pelycosauria 
to  one  postorbital  arch  of  the  skull,  and  this  is  the  zy- 
gomatic  of  the  Mammalia.  In  both  Reptilia  and  Mam- 
malia (excepting  Prototheria  and  Procolophonina3)  the 
coracoid  element  is  of  reduced  size,  and  is  co-ossified 
with  the  scapula.  In  both  (except  Cotylosauria)  the 
capitular  articulation  of  the  ribs  is  intercentral.  In 
both  the  humerus  has  distal  condyles  and  epicondyles, 
and  there  is  an  entepicondylar  foramen  in  the  Pelyco- 
sauria as  in  the  lower  Mammalia.  The  posterior  foot 

1  See  The  Evolution  of  the  Vertebrata  Progressive  and  Retrogressive;  Amer. 
Naturalist,  1885.     Dohrn,    Der    Ursprung  der   Wirbelthiere  und  das  Princip 
dcs  Functionwechsels,  Leipsic,  1875.     "  On  the  Phylogeny  of  the  Vertebrata," 
Cope,  American  Naturalist,  Dec.,  1884.     See  also  the  following  references: 
American  Naturalist,  1884,  p.  1136 ;  Proceedings  of  the  Academy  of  Philadelphia, 
1867,  p.  234  ;  Proceedings  American  Philosophical  Society,  1884,  p.  585  ;  American 
Naturalist,  1884,  p.  27;  Proceedings  American  Association  for  the  Advancement 
of  Science,  XIX,  1871,  p.  233  ;  Proceedings  American  Philosophical  Society ,  1882,  p. 
447;  American  Naturalist,  1884,  pp.  261  and  1121 ;  Report  U.  S.  Geol.  Survey  W. 
of  root h  Mer.,  G.  M.  Wheeler,  1877,  IV,  2,  p.  282. 

2  Proceedings  American  Philosophical  Society,  1884,  p.  43. 

3  Seeley,  Philos.  Trans.  Royal  Society,  1889,  269. 


88     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

is  constructed  in  the  Pelycosauria  almost  exactly  like 
that  of  the  Prototheria.  The  single  occipital  condyle 
of  the  reptiles  is  not  found  in  the  Mammalia,  but  in 
some  of  the  Lacertilia  (Uroplates,  Gecco)  there  are 
two  condyles,  the  median  (basioccipital)  portion  of  the 
single  condyle  being  rudimental,  and  Seeley  has  re- 
cently shown  that  it  is  deeply  divided  at  the  middle  in 
the  Permian  Cynognathidae  of  South  Africa..  The 
Pelycosauria  could  not,  however,  have  given  origin  to 
the  Prototheria,  since  in  that  subclass  of  mammals  there 
is  a  well-developed  coracoid.  But  in  the  Procolopho- 
nina  this  element  is  developed  as  in  the  Prototheria. 
Moreover,  the  Pelycosauria  and  the  Procolophonina 
have  the  interclavicle,  which  is  an  element  of  membran- 
ous origin,  while  in  the  Prototheria  we  have  the  corre- 
sponding cartilage  bone,  the  episternum.  This  element 
is'  present  in  the  Permian  order  of  the  Cotylosauria, 
which  is  nearly  related  to  the  Pelycosauria.  This  or- 
der has,  however,  single-headed  ribs,  springing  from 
the  diapophyses,  which  is  not  usual  in  the  Mammalia. 
But  in  some  Cotylosauria  the  diapophyses  are  short, 
and  in  the  Monotremata  the  postcervical  ribs  are  sin- 
gle-headed, so  this  character  is  not  an  insurmountable 
one.  It  is  evident  that  the  Mammalia  were  derived 
from  some  type  probably  referable  to  a  Permian  rep- 
tilian order  of  the  Theromorous  series,  although  to 
which  one  is  not  yet  known. 

The  Reptilia  have  been  supposed  by  Haeckel  to 
have  taken  their  origin  from  the  Batrachia.  I  have 
indicated  that  it  is  probable  that  the  batrachian  order, 
which  stands  in  this  relation  to  the  Reptilia,  is  the 
Embolomeri  of  the  Permian  epoch.  This  conclusion 
rests  on  the  following  considerations.  The  reptilian 
order  of  the  Cotylosauria  approaches  the  Batrachia  of 


PHYLOGENY.  89 

the  subclass  Stegocephali  in  the  overroofing  of  the 
posterior  regions  of  the  skull ;  in  the  presence  of  vo- 
merine  teeth,  and  in  the  absence  of  obturator  foramen 
of  the  pelvis.  In  some  Cotylosauria  (Diadectidae)  the 
stegocephalian  tabular  bone  of  the  skull  is  well  devel- 
oped. But  in  the  Cotylosauria,  the  vertebral  column 
consists  mainly  of  centra,  while  in  the  Stegocephali  it 
consists  entirely  or  partly  of  intercentra.  But  in  the 
Embolomeri  the  centra  are  well  developed,  and  are 
larger  than  the  intercentra  anterior  to  the  pelvis. 
Hence  this  is  the  only  order  of  Stegocephali  from 
which  the  Reptilia  could  have  been  derived. 

Haeckel  derived  the  Batrachia  from  the  Dipnoi 
(Dipneusta),  and  I  followed  him  in  this  belief,  being 
strengthened  in  it  by  Huxley's  ascription  of  an  auto- 
stylic  suspensorium  of  the  mandible1  to  both  divisions. 
This  phylogeny  is  questioned  by  Pollard2  and  by  Kings- 
ley,3  who  would  see  the  ancestry  of  the  Batrachia  in 
the  crossopterygian  fishes  on  embryological  grounds 
derived  from  a  study  of  Polypterus.  In  support  of 
their  view  I  would  cite  the  absence  of  the  maxillary 
arch  in  the  Dipnoi,  and  its  full  development  in  the 
Stegocephali,  which  are  the  ancestral  Batrachia.  The 
large  development  of  the  dorsal  and  anal  fins  in  the 
Dipnoi  is  not  favorable  to  the  Haeckelian  view ;  nor 
do  the  paired  fins  approach  as  nearly  to  the  limbs  of 
Batrachia  as  do  those  of  some  other  fishes.  It  has  been 
shown  by  Huxley  that  the  suspensorium  of  the  Ba- 
trachia is  hyostylic  in  its  earliest  stages,  and  that  it 
becomes  autostylic  at  a  later  period  of  development. 

1  Proceedings  Zodlogical  Society  of  London,  1876,  p.  59. 
1  Anatomischer  Anzeiger,  VI,  p.  338,  1891. 

3  American  Naturalist,  1892,  p.  679.     Kingsley  would  also  derive  the  Dip- 
noi from  Crossopterygia. 


9o    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


PHYLOGENY.  91 

The  Batrachia  may  then  have  originated  from  a  hyo- 
stylic  teleostomous  (i.  e.,  one  with  complete  maxillary 
arch)  fish.  Among  Teleostomata  we  naturally  look  for 
forms  with  limbs  which  approach  nearest  the  batrachian 
type,  and  in  which  median  fins  are  feeble  or  wanting. 
Such  are  the  Rhipidopterygia  (formerly  included  in 
the  Crossopterygia),  which  include  the  families  of 
Holoptychiidae,  Tristichopteridae,  Osteolepididae,  Coe- 
lacanthidae,  and  perhaps  some  others.  These  fam- 
ilies, except  the  last,  abounded  in  the  waters  of  the 
Devonian  period,  at  the  time  when  the  ancestors  of 
the  Batrachia  also  existed.  All  of  them  agree  in  pos- 
sessing the  median  fins  of  greatly  reduced  proportions, 
and  the  mesodermal  or  internal  elements  of  the  paired 
fins  more  like  the  limbs  of  the  Batrachia  than  are  those 
of  any  known  fishes.  The  constitution  of  the  superior 
cranial  wall  is  a  good  deal  like  that  of  the  stegocepha- 
lous  Batrachia.  The  characters  of  the  fins  can  be 
learned  from  the  accompanying  figure  of  the  Eusthe- 
nopterumfoordiiVJ\\ite2iVes,  one  of  the  Tristichopteridae. 
The  pectoral  fin  well-nigh  realizes  Gegenbaur's  theory 
of  the  derivation  of  the  Chiropterygium  from  the  Ar- 
chipterygium. 

The  ancestral  type  of  fishes  is  probably  the  acan- 
thodean  order  of  the  subclass  of  sharks  (Elasmo- 
branchii).1  Like  other  sharks,  they  are  hyostylic  and 
have  no  maxillary  arch  or  cranial  bones.  They  have 
the  ptychopterygium,  which  is  the  primitive  type  of 
fin.  In  this  fin  the  osseous  elements  which  support 
the  fin- rays  are  enclosed  within  the  body- wall,  the  rays 
only  being  free.  Such  a  fin  sustains  the  hypothesis 
that  the  paired  fins  are  parts  of  primitively  continuous 

1  As  represented  by  the  Cladodontidae ;  see  Dean,   Trans.  N.  Y.  Acad. 
Set.,  1893.  p.  124,  and  Cope,  American  Naturalist,  1893,  p.  999. 


92     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

longitudinal  folds.  This  hypothesis  is  further  sus- 
tained by  the  acanthodean  genus  Climatius,  where  a 
series  of  spines  intervenes  between  the  paired  fins  in 


line  with  them.  From  what  the  Acanthodeans  can 
have  been  descended  is  at  present  conjectural.  They 
trace  their  ancestry  ultimately  to  Branchiostoma  (Am- 
phioxus)  through  forms  not  yet  discovered.  This  ge- 


PHYLOGENY.  93 

nus  represents  the  class  Acrania,  which  is  the  ancestor 
of  craniate  Vertebrata. 

The  phylogeny  of  the  Vertebrata  may  be  repre- 
sented diagrammatically  as  follows  : 


Aves 


Teliostomata  (other! 


TeteStomata  (Rhipidopterygia) 

Elasmobr.  (Selachii) 
Hlasmo  >ranchii—  Acanthodii 

Agi  atha 
Tunicata  Acrania  Enteropneusta 

The  Vertebrata  exhibit  the  most  unmistakable  gra- 
dation in  the  characters  of  the  circulatory  system.  It 
has  long  been  the  custom  to  define  the  classes  by  means 
of  these  characters,  taken  in  connection  with  those  of 
the  skeleton.  Commencing  in  the  Leptocardii  with 
the  simple  tube,  we  have  two  chambers  in  the  Marsi- 
pobranchii  and  fishes  ;  three  in  the  Batrachia  and  Rep- 
tilia  ;  and  four  in  the  Aves  and  Mammalia.  The  aorta- 
roots  commence  as  numerous  pairs  of  branchial  arter- 
ies in  the  Leptocardii ;  we  see  seven  in  the  Marsipo- 
branchi,  five  in  the  fishes  (with  number  reduced  in 
some)  ;  four  and  three  in  Batrachia,  where  they  gen- 
erally cease  to  perform  branchial  functions  ;  two  and 
one  on  each  side  in  Reptilia  ;  the  right-hand  one  in 
birds,  and  the  left-hand  one  in  Mammalia.  This  order 
is  clearly  an  ascending  one  throughout.  It  consists 
of,  first,  a  transition  from  adaptation  to  an  aquatic,  to 


94     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

an  aerial  respiration ;  and,  second,  an  increase  in  the 
power  to  aerate  and  distribute  a  circulating  fluid  of  in- 
creased quantity,  and  of  increased  calorific  capacity. 
In  other  words,  the  circulation  passes  from  the  cold  to 
the  hot-blooded  type  coincidentally  with  the  changes 
of  structure  above  enumerated.  The  accession  of  a  ca- 
pacity to  maintain  a  fixed  temperature  while  that  of 
the  surrounding  medium  changes,  is  an  important  ad- 
vance in  animal  economy. 

The  brain  and  nervous  system  also  display  a  gen- 
eral progressive  ascent.  Leaving  the  brainless  Acrania, 
the  Marsipobranchs  and  fishes  present  us  with  small 
hemispheres  with  thin  cortex,  larger  optic  lobes,  and 
well-developed  cerebellum.  The  hemispheres  are  really 
larger  than  they  appear  to  be,  as  Rabl  Riickard  has 
shown l  that  the  supposed  hemispheres  are  only  corpora 
striata.  But  the  superior  walls  are  membranous,  and 
support  on  their  internal  side  only  a  layer  of  epithelial 
cells,  as  in  the  embryos  of  other  Vertebrata,  instead  of 
the  gray  substance.  So  that,  although  we  find  that  the 
cerebellum  is  really  smaller  in  the  Batrachia  and  most 
Reptilia  than  in  the  fishes,  the  better  development  of 
the  hemispheres  in  the  former  gives  them  the  pre- 
eminence. The  Elasmobranchii  show  themselves  su- 
perior to  many  of  the  fishes  in  the  large  size  of  their 
corpora  restiformia  and  cerebellum.  The  Reptilia  con- 
stitute an  advance  on  the  Batrachia.  In  the  latter  the 
optic  thalami  are,  with  some  exceptions,  of  greater 
diameter  than  the  hemispheres,  while  the  reverse  is 
generally  true  of  the  reptiles.  The  crocodiles  display 
much  superiority  over  the  other  reptiles  in  the  larger 
cerebellum,  with  rudimental  lateral  lobes.  The  greater 
development  of  the  hemispheres  in  birds  is  well  known, 

\Biologisches  Centralblatt,  1884,  p.  449. 


PHYLOGENY.  95 

while  the  general  superiority  of  the  brain  of  the  living 
Mammalia  over  all  other  vertebrates  is  admitted. 

The  consideration  of  the  successive  relations  of  the 
skeleton  in  the  classes  of  vertebrates  embraces,  of 
course,  only  the  characters  which  distinguish  those 
classes.  These  are  not  numerous.  They  embrace  the 
structure  of  the  axis  of  the  skull ;  of  the  ear-bones  ;  of 
the  suspensors  of  the  lower  jaw ;  of  the  scapular  arch 
and  anterior  limb,  and  of  the  pelvic  arch  and  posterior 
limb.  Other  characters  are  numerous,  but  do  not  enter 
into  consideration  at  this  time. 

The  persistence  of  the  primitive  cartilage  in  any 
part  of  the  skeleton  is,  embryologically  speaking,  a 
mark  of  inferiority.  From  a  physiological  or  functional 
standpoint  it  has  the  same  significance,  since  it  is  far 
less  effective  both  for  support  and  for  movement  than 
is  the  segmented  osseous  skeleton.  That  this  is  a  prev- 
alent condition  of  the  lower  Vertebrata  is  well  known. 
The  bony  fishes  and  Batrachia  have  but  little  of  the 
primitive  cartilage  remaining,  and  the  quantity  is  still 
more  reduced  in  the  higher  classes.  Systematically, 
then,  the  vertebrate  series  is  in  this  respect  an  ascend- 
ing one.  The  Acrania  are  membranous ;  the  Marsi- 
pobranchii  and  most  of  the  Elasmobranchii  cartilagi- 
nous ;  the  other  Pisces  and  the  Batrachia  have  the 
basicranial  axis  cartilaginous,  so  that  it  is  not  until  the 
Reptilia  are  reached  that  we  have  osseous  sphenoid 
and  presphenoid  bones,  such  as  characterize  the  birds 
and  mammals.  The  vertebral  column  follows  more  or 
less  inexactly  the  history  of  the  base  of  the  skull,  but 
its  characters  do  not  define  the  classes. 

As  regards  the  suspensor  of  the  lower  jaw,  the  scale 
is  in  the  main  ascending.  We  witness  a  gradual  change 
in  the  segmentation  of  the  mandibular  visceral  arch  of 


96     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

the  skull,  which  clearly  has  for  its  object  such  a  con- 
centration of  the  parts  as  will  produce  the  greatest  ef- 
fectiveness of  the  biting  function.  This  is  accom- 


plished by  reducing  the  number  of  the  segments,  so  as 
to  bring  the  resistance  of  the  teeth  nearer  to  the  power, 
that  is,  the  masseter  and  related  muscles,  and  their 
base  of  attachment,  the  brain-case.  This 


is  seen  in 


PHYLOGENY.  97 

bony  vertebrates  in  the  reduction  of  the  segments  be- 
tween the  lower  jaw  proper  and  the  skull,  from  four  to 
none.  In  the  fishes  we  have  the  hyomandibular,  the 
symplectic,  the  inferior  quadrate,  and  the  articular. 
In  the  Batrachia,  reptiles  and  birds,  we  have  the  quad- 
rate and  articular  only,  while  in  the  Mammalia  these 
elements  also  are  wanting. 

The  examination  of  the  pectoral  and  pelvic  arches 
reveals  a  successive  modification  of  the  adaptation  of 
the  parts  to  the  mechanical  needs  of  the  limbs.  In 
this  regard  the  air-breathing  types  display  wide  di- 
versity from  the  gill-bearing  types  or  fishes.  In  the 
latter,  the  lateral  elements  unite  below  without  the  in- 
tervention of  a  median  element  or  sternum,  while  in 
the  former  the  sternum,  or  parts  of  it,  is  generally  pres- 
ent. Either  arrangement  is  susceptible  of  much  me- 
chanical strength,  as  witness  the  siluroid  fishes  on  the 
one  hand,  and  the  mole  on  the  other.  The  numerous 
segments  of  the  fishes'  pectoral  arch  must,  however, 
be  an  element  of  weakness,  so  that  from  a  mechanical 
standpoint  it  must  take  the  lowest  place.  The  pres- 
ence of  sternal  elements,  with  both  clavicle,  epicora- 
coid,  and  coracoid  bones  on  each  side,  gives  the  Rep- 
tilia  the  highest  place  for  mechanical  strength.  The 
loss  of  the  bony  coracoid  seen  in  the  tailed  Batrachia, 
and  loss  of  coracoid  and  epicoracoid  in  the  Mammalia, 
constitute  an  element  of  weakness.  The  line  is  not 
then  one  of  uniform  ascent  in  this  respect. 

The  absence  of  pelvis,  or  its  extremely  rudimental 
condition,  in  fishes,  places  them  at  the  foot  of  the  line 
in  this  respect.  The  forward  extension  of  the  ilium  in 
some  Batrachia  and  in  the  Mammalia,  is  to  be  com- 
pared with  its  backward  direction  in  Reptilia,  and  its 
extension  both  ways  in  the  birds.  These  conditions 


98     PR  t MAR  Y  FA  CTORS  OF  ORGANIC  E VOL  UT1ON. 

are  all  derived  by  descent  from  a  strictly  intermediate 
position  in  the  Batrachia  and  Reptilia  of  the  Permian 
epoch.  The  anterior  direction  must  be  regarded  as 
having  the  mechanical  advantage  over  the  posterior 
direction,  since  it  shortens  the  vertebral  column  and 
brings  the  grip  of  the  posterior  nearer  to  the  anterior 
feet.  The  prevalence  of  the  latter  condition  in  the 
Mammalia  enables  them  to  stand  clear  of  the  ground, 
while  the  Reptilia  move  with  the  abdomen  resting  upon 
it,  excepting  the  higher  Dinosauria,  where  the  arrange- 
ment is  as  in  birds.  As  regards  the  inferior  arches  of 
the  pelvis,  the  Mammalia  have  the  advantage  again, 
in  the  strong  bony  median  symphysis  connecting  the 
ischium  and  pubis.1  This  character,  universal  among 
the  land  Vertebrata  of  the  Permian  epoch,  has  been  lost 
by  the  modern  Reptilia  and  birds,  and  is  retained  only 
by  the  Mammalia.  So  the  lines,  excepting  the  mam- 
malian, have  degenerated  in  every  direction  in  the  char- 
acters of  the  pelvis. 

The  limbs-of  the  Pisces  are  as  well  adapted  to  their 
environment  as  are  those  of  the  land  Vertebrata ;  but, 
from  an  embryological  standpoint,  their  structure  is 
inferior.  The  primitive  rays  are  less  modified  in  the 
fin  than  in  the  limb  ;  and  limbs  themselves  display  a 
constantly  increasing  differentiation  of  parts,  com- 
mencing with  the  Batrachia  and  ending  with  the  Mam- 
malia. The  details  of  these  modifications  belong  to 
the  history  of  the  contents  of  the  classes,  however, 
rather  than  to  the  succession  of  the  Vertebrata  as  a 
whole. 

In  review,  it  may  be  said  that  a  comparison  of  the 
characters  which  define  the  classes  of  the  vertebrates 
shows  that  this  branch  of  the  animal  kingdom  has 

IThis  is  an  advantage  as  a  protection  during  gestation. 


PHYLOGENY.  99 

made  with  the  ages  successive  steps  of  progress  from 
lower  to  higher  conditions.  This  progress  has  not  been 
without  exception,  since,  as  regards  the  construction 
of  the  scapular  arch,  the  Mammalia  have  retrograded 
from  the  reptilian  standard  as  a  whole. 

In  subsequent  pages  I  shall  take  up^the  lines  of  the 
classes  separately. 

b.    The  Line  of  the  Pisces. 

The  fishes  form  various  series  and  subseries,  and 
the  tracing  of  all  of  them  is  not  yet  practicable,  owing 
to  the  deficiency  in  our  knowledge  of  the  earliest  or 
ancestral  forms.  Thus  the  origins  of  the  three  sub- 
classes, Holocephali,  Dipnoi,  and  Elasmobranchii,  are 
lost  in  the  obscurity  of  the  early  Paleozoic  ages.  The 
genus  Paleospondylus  of  Traquair  from  the  Carbonife- 
rous probably  represents  an  Agnathous  type  from 
which  all  fishes  may  have  sprung,  although  the  genus, 
as  now  known,  has  not  sufficient  antiquity  to  claim 
this  place.  It  may  be  a  near  descendant  of  the  amphi- 
oxus. 

A  comparison  of  the  four  subclasses  of  fishes  shows 
that  they  are  related  in  pairs.  The  Holocephali  and 
Dipnoi  have  no  distinct  suspensory  segment  for  the 
lower  jaw,  while  the  Elasmobranchii  and  Teleostomata 
have  such  a  separate  element.  The  latter,  therefore, 
present  one  step  in  the  direction  of  complication  be- 
yond the  former.  It  is,  however,  asserted  by  Huxley1 
that  the  absence  of  suspensorium  is  due  to  its  appro- 
priation by  the  hyoid  arch  in  the  Holocephali,  and  its 
rudimental  condition  in  the  Dipnoi.  If  this  be  the 
case,  the  Holocephali  and  Dipnoi  are  peculiar  speciali- 

1  Proceedings  Zoological  Society,  London,  1876,  p.  45. 


ioo    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

zations  at  one  side  of  the  main  line  of  descent  of  the 
fishes.  We  look  then  for  the  ancestral  type  of  the  true 
fishes  among  the  Elasmobranchii,  and  of  these  the 
Ichthyotomi  display  the  greatest  resemblances  to  the 
Teleostomata  in  all  respects.1 

Too  little  is  known  of  the  history  of  the  subclasses, 
excepting  the  Teleostomata,  for  us  to  be  able  to  say 
much  of  the  direction  of  the  descent  of  their  contained 
orders.  On  the  sharks  much  light  is  shed  by  the  dis- 
covery of  characters  of  the  genus  Cladodus  Agass.,  in 
which  the  support  of  the  paired  fins  consists  of  a  meta- 
pterygium,  which  is  enclosed  in  a  lateral  fold  of  the 
body  wall,  and  which  gives  rise  to  simple  external 
basilar  rods  only.  Of  the  Teleostomata  a  much  clearer 
history  is  accessible.  It  has  four  primary  divisions  or 
tribes  which  differ  solely  in  the  structure  of  the  sup- 
ports of  the  fins.  In  the  first  division,  the  Crossopte- 
rygia,  the  anterior  limbs  have  numerous  basilar  bones 
which  are  supported  on  a  peduncle  of  axial  bones. 
The  posterior  limbs  are  similar.  In  the  second  divi- 
sion, or  Podopterygia  (the  sturgeons,  etc.),  the  pos- 
terior limbs  remain  the  same,  while  the  anterior  limbs 
have  undergone  a  great  abbreviation  in  the  loss  of  the 
axial  bones  and  the  reduction  of  the  number  and  length 
of  the  basilar  bones.  In  the  third  group,  or  Actino- 
pterygia,  both  limbs  have  undergone  reduction,  the 
basilar  bones  in  the  posterior  fin  being  almost  all  atro- 
phied, while  those  of  the  fore  limb  are  much  reduced 
in  number.  In  the  fourth  superorder,  the  Rhipido- 
pterygia,  the  axial  supports  of  the  median  fins  are 
greatly  reduced  in  number,  presenting  a  marked  con- 
trast to  the  other  superorders  ;  while  the  axial  elements 

1  See  Proceedings  American  Philosophical  Society,  1884,  p.  572,  on  the  genus 
Didymodus. 


PHYLOGENY.  ,  _joj 

of  the  paired  fins  are  present  and  primitive,  and  re- 
semble those  of  one  of  the  suborders  of  sharks. 

The  phylogeny  of  the  Teleostomata,  as  indicated 
by  the  fin-structure,  will  commence  with  the  Crosso- 
pterygia.  From  this  group  the  Podopterygia  may  be 
theoretically  derived,  and  from  these  the  Actinoptery- 
gia.  The  Rhipidopterygia  appear  to  be  a  side  group, 
not  in  the  main  piscine  line.  But  the  oldest  known 
Crossopterygia  are  from  the  Carboniferous,  while  the 
Rhipidopterygia  are  abundant  in  the  Devonian.  More- 
over, the  superorder  Actinopterygia,  with  its  contracted 
fins,  may  have  appeared  in  the  Carboniferous,  while 
the  Podopterygia  (Palaeoniscidae)  certainly  did  so. 

The  descent  of  the  fishes  in  general  has  witnessed, 
then,  a  contraction  of  the  limbs  to  a  very  small  com- 
pass, and  their  substitution  by  a  system  of  accessory 
dermal  radii.  This  has  been  an  ever-widening  diver- 
gence from  the  type  of  the  higher  Vertebrata,  and 
from  this  standpoint,  and  also  a  view  of  the  "loss  of 
parts  without  complementary  addition  of  other  parts," 
may  be  regarded  as  a  process  of  degeneration. 

Taking  up  the  great  division  of  the  Actinopterygia, 
which  embraces  most  of  the  species  of  living  fishes, 
we  can  trace  the  direction  of  descent  largely  by  ref- 
erence to  their  systematic  relations  when  we  have  no 
fossils  to  guide  us. 

The  three  subtribes  adopted  by  Jordan  represent 
three  series  of  the  true  fishes  which  indicate  lines  of 
descent.  The  Holostei  include  the  remainder  of  the 
old  ganoids  after  the  subtraction  of  the  Rhipidoptery- 
gia, the  Crossopterygia,  and  the  Podopterygia.  They 
resemble  these  forms  in  the  muscular  bulbus  arteriosus 
of  the  heart,  in  the  chiasm  of  the  optic  nerves,  and  in 
the  greater  distinctness  of  the  metapterygium.  The 


FACTORS  OF  ORGANIC  EVOLUTION 

two  former  characters  are  complexities  which  the  two 
other  divisions  do  not  possess,  and  which,  as  descend- 
ants coming  later  in  time,  must  be  regarded  as  inferior, 
and  therefore  to  that  extent  degenerate.  Of  these  di- 
visions the  Malacopterygia  approach  nearest  the  Ho- 
lostei,  and  are  indeed  not  distinctly  definable  without 
exceptions.  The  third  division,  or  Acanthopterygia, 
shows  a  marked  advance  beyond  the  others  in  :  (i)  the 
obliteration  of  the  primitive  trachea,  or  ductus  pneu- 
maticus,  which  connects  the  swim-bladder  and  oeso- 
phagus ;  (2)  the  advance  of  the  ventral  fins  from  the 
abdomen  forward  to  the  throat ;  (3)  the  separation  of 
the  parietal  bones  by  the  supraoccipjtal ;  (4)  the  pres- 
ence of  numerous  spinous  rays  in  the  fins  ;  and  (5)  the 
roughening  of  the  edges  of  the  scales,  forming  the  cten- 
oid type.  There  are  more  or  less  numerous  excep- 
tions to  all  of  these  characters.  The  changes  are  all 
further  divergencies  from  the  other  vertebrate  classes, 
or  away  from  the  general  line  of  ascent  of  the  verte- 
brate series  taken  as  a  whole.  The  end  gained  is  spe- 
cialization ;  but  whether  the  series  can  be  called  either 
distinctively  progressive  or  retrogressive,  is  not  so 
clear.  The  development  of  osseous  spines,  rough 
scales,  and  other  weapons  of  defense,  together  with 
the  generally  superior  energy  and  tone  which  prevail 
among  the  Acanthopterygia,  characterize  them  as  su- 
perior to  the  Malacopterygia,  but  their  departure  from 
the  ascending  line  of  the  Vertebrata  has  another  ap- 
pearance. 

The  descent  of  the  Acanthopterygian  fishes  has 
probably  been  from  Holostean  ancestors,  both  with 
and  without  the  intervention  of  Malacopterygian  forms. 
This  is  indicated  by  increase  in  the  number  of  basilar 


PHYLOGENY.  103 

bones1  in  the  fins  of  families  which  have  pectoral  ven- 
tral fins,  and  in  the  extinct  genus  Dorypterus.2 

The  Malacopterygia  display  three  or  four  distinct 
lines  of  descent.  The  simplest  type  is  represented  by 
the  order  Isospondyli,  and  paleontology  indicates  clearly 
that  this  order  is  also  the  oldest,  as  it  dates  from  the 
Trias  at  least.  In  one  line  the  anterior  dorsal  verte- 
brae have  become  complicated,  and  form  an  interlock- 
ing mass  which  is  intimately  connected  with  the  sense 
of  equilibrium  in  the  water.  This  series  commences 
with  the  Characinidae,  passes  through  the  Cyprinidae, 
and  ends  with  the  Siluridae.  The  arrangements  for 
equilibration  constitute  a  superadded  complication, 
and  to  these  are  added  in  the  Siluroids  defensive  spines 
and  armor.  Some  of  this  order,  however,  are  distinctly 
degenerate,  as  the  soft  purblind  Ageniosus,  and  the 
parasitic  Stegophilus  and  Vandellia,  which  are  nearly 
blind,  without  weapons,  and  with  greatly  reduced  fins. 

The  next  line  (the  Haplomi,  pike,  etc.)  loses  the 
precoracoid  arch  and  has  the  parietal  bones  separated, 
both  characters  of  the  Acanthopterygia.  This  group 
was  apparently  abundant  during  the  Cretaceous  period, 
and  it  may  have  given  origin  to  many  of  the  Acantho- 
pterygia. 

Another  line  also  loses  the  precoracoid,  but  in  other 
respects  diverges  totally  from  the  Acanthopterygia  and 
all  other  Malacopterygia.  This  is  the  line  of  the  eels. 
They  next  lose  the  connection  between  the  scapular 
arch  and  the  skull,  which  is  followed  by  the  loss  of  the 
pectoral  fin.  The  ventral  fin  disappeared  sooner.  The 
palatine  bones  and  teeth  disappear,  and  the  suspensor 

1  See  Cope  "  On  the  Homologies  of  the  Fins  of  Fishes  "  ;    American  Nat- 
uralist, 1890,  p.  401. 

2  See  Proceedings  of  the  American  Association  for  the  Advancement  of  Sci- 
ence, 1878,  p.  297. 


104    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

of  the  lower  jaw  grows  longer  and  loses  its  symplectic 
element.  The  opercular  bones  grow  smaller,  and  some 
of  them  disappear.  The  ossification  of  most  of  the 
hyoid  elements  disappears,  and  some  of  their  cartila- 
ginous bases  even  vanish.  These  forms  are  the  marine 
eels  or  Colocephali.  The  most  extraordinary  example 
of  specialization  and  degeneracy  is  seen  in  the  abyssal 
eels  of  the  family  Eurypharyngidae.  Here  all  the  de- 
generate features  above  mentioned  are  present  in  ex- 
cess, and  others  are  added,  as  the  loss  of  ossification 
of  a  part  of  the  skull,  almost  total  obliteration  of  the 
hyoid  and  scapular  arches,  and  the  semi-notochordal 
condition  of  the  vertebral  column,  etc. 

The  Acanthopterygia  nearest  the  Malacopterygia 
have  abdominal  ventral  fins,  and  belong  to  several  or- 
ders. It  is  such  types  as  these  that  may  be  supposed 
to  have  been  derived  directly  from  Holostean  ances- 
tors. They  appear  in  the  Cretaceous  period  (Derce- 
tidae),  along  with  the  types  that  connect  with  the  Ma- 
lacopterygia (Haplomi).  Intermediate  forms  between 
these  and  typical  Acanthopterygii  occur  in  the  Eocene 
(Trichophanes,  Erismatopterus),  showing  several  lines 
of  descent.  The  Dercetidae  belong  apparently  to  the 
order  Hemibranchi,  while  the  Eocene  genera  named 
belong  apparently  to  the  Aphododiridae,  the  immediate 
ancestor  of  the  highest  Physoclysti,  the  Percomorphi. 
The  order  Hemibranchi  is  a  series  of  much  interest. 
Its  members  lose  the  membrane  of  their  dorsal  spinous 
fin  (Gasterosteidae),  and  then  the  fin  itself  (Fistularia, 
Pegasus).  The  branchial  apparatus  has  undergone, 
as  in  the  eels,  successive  deossification  (by  retarda- 
tion), and  this  in  direct  relation  to  the  degree  with 
which  the  body  comes  to  be  protected  by  bony  shields, 
reaching  the  greatest  defect  in  the  Amphisilidae.  One 


PHYLOGENY.  105 

more  downward  step  is  seen  in  the  next  succeeding 
order  of  the  Lophobranchii.  The  branchial  hyoid  ap- 
paratus is  reduced  to  a  few  cartilaginous  pieces,  and  the 
branchial  fringes  are  much  reduced  in  size.  In  the 
Hippocampidae  the  caudal  fin  disappears  and  the  tail 
becomes  a  prehensile  organ  by  the  aid  of  which  the 
species  lead  a  sedentary  life.  The  mouth  is  much  con- 
tracted and  becomes  the  anterior  orifice  of  a  suctorial 
tube.  This  is  a  second  line  of  unmistakable  degen- 
eracy among  true  fishes. 

The  Acanthopterygia  with  pectoral  ventral  fins  pre- 
sent us  with  perhaps  ten  important  ordinal  or  subordi- 
nal  divisions.  Until  the  paleontology  of  this  series  is 
better  known,  we  shall  have  difficulty  in  constructing 
phylogenies.  Some  of  the  lines  may,  however,  be 
made  out.  The  accompanying  diagram  will  assist  in 
understanding  them. 

The  Anacanthini  present  a  general  weakening  of 
the  organization  in  the  less  firmness  of  the  osseous 
tissue  and  the  frequent  reduction  in  the  size  and  char- 
acter of  the  fins.  The  caudal  vertebrae  are  of  the 
diphycercal  type.  As  this  group  does  not  appear  early 
in  geological  time,  and  as  it  is  largely  represented  now 
in  the  abyssal  ocean  fauna,  there  is  every  reason  to 
regard  it  as  a  degenerate  type.1  The  Heterosomata 
(flounders)  found  it  convenient  to  lie  on  one  side,  a 
habit  which  would  appear  to  result  from  a  want  of  mo- 
tive energy.  The  fins  are  very  inefficient  organs  of 
movement  in  them,  and  they  are  certainly  no  rivals  for 
swift-swimming  fishes  in  the  struggle  for  existence, 
excepting  as  they  conceal  themselves.  In  order  to  see 
the  better  while  unseen,  the  inferior  eye  has  turned  in- 

IThe  general  characters  of  the  deep-sea  fish-fauna  are  those  of  degen- 
eracy. 


106    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

ward,  i.  e.,  upward,  and  finally  has  penetrated  to  the 
superior  surface,  so  that  both  eyes  are  on  one  side.  This 
peculiarity  would  be  incredible,  if  we  did  not  know  of 


its  existence,  and  is  an  illustration  of  the  extraordinary 
powers  of  accommodation  possessed  by  nature.  The 
Heterosomata  (flatfishes)  can  only  be  considered  a  de- 
generate group.  The  scyphobranch  line  presents  a 


PHYLOGENY.  107 

specialization  of  the  superior  pharyngeal  bones,  which 
is  continued  by  the  Haplodoci  (Batrachidae).  This 
cannot  be  called  a  degenerate  line,  although  the  fin- 
rays  are  soft. 

The  double  bony  floor  of  the  skull  of  the  distegous 
percomorph  fishes  is  a  complication  which  places  them 
at  the  summit  of  the  line  of  true  fishes.  At  the  sum- 
mit of  this  division  must  be  placed  the  Pharyngogna- 
thi,  which  fill  an  important  role  in  the  economy  of  the 
tropical  seas,  and  the  fresh  waters  of  the  Southern 
Hemisphere.  By  means  of  their  powerful  grinding 
pharyngeal  apparatus  they  can  reduce  vegetable  and 
animal  food  inaccessible  to  other  fishes.  The  result 
is  seen  in  their  multifarious  species  and  innumerable 
individuals  decked  in  gorgeous  colors,  and  often  reach- 
ing considerable  size.  This  is  the  royal  suborder  of 
fishes,  and  there  is  no  reason  why  they  should  not  con- 
tinue to  increase  in  importance  in  the  present  fauna. 

Very  different  is  the  line  of  the  Plectognathi.  The 
probable  ancestors  of  this  division,  the  Epelasmia 
(Chaetodontidae,  etc.),  are  also  abundant  in  the  tropi- 
cal seas,  and  are  among  the  most  brilliantly  colored  of 
fishes.  One  of  their  peculiarities  is  seen  in  a  shorten- 
ing of  the  brain-case  and  prolongation  of  the  jaws 
downward  and  forward.  The  utility  of  this  arrange- 
ment is  probably  to  enable  them  to  procure  their  food 
from  the  holes  and  cavities  of  the  coral  reefs,  among 
which  they  dwell.  In  some  of  the  genera  the  muzzle 
has  become  tubular  (Chelmo),  and  is  actually  used  as 
a  blow-gun  by  which  insects  are  secured  by  shooting 
them  with  drops  of  water.  This  shortening  of  the 
basicranial  axis  has  produced  a  corresponding  abbre- 
viation of  the  hyoid  apparatus.  The  superior  pharyn- 
geal bones  are  so  crowded  as  to  have  become  a  series 


io8    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

of  vertical  plates  like  the  leaves  of  a  book.  These 
characters  are  further  developed  in  the  Plectognathi. 
The  brain- case  is  very  small,  the  face  is  very  elongate, 
and  the  mouth  is  much  contracted.  The  bones  sur- 
rounding it  in  each  jaw  are  coossified.  The  axial  ele- 
ments (pubes)  of  the  posterior  fins  unite  together,  be- 
come very  elongate,  and  lose  the  natatory  portion.  In 
one  group  (Orthagoriscidae)  the  posterior  part  of  the 
vertebral  column  is  lost,  and  the  caudal  fin  is  a  nearly 
useless  rudiment.  In  the  Ostraciontidae  (which  may 
have  had  a  different  origin,  as  the  pharyngeal  bones 
are  not  contracted)  the  natatory  powers  are  much  re- 
duced, and  the  body  is  inclosed  in  an  osseous  carapace 
so  as  to  be  capable  of  very  little  movement.  The  en- 
tire order  is  deficient  in  osseous  tissue,  the  bones  be- 
ing thin  and  weak.  It  is  a  marked  case  of  degeneracy. 

There  are  several  evident  instances  of  sporadic  de- 
generacy in  other  orders.  One  of  these  is  the  case  of 
the  family  of  the  Icosteidae,  fishes  from  deep  waters  off 
the  coast  of  California.  Although  members  of  the 
Percomorphi,  the  skeleton  in  the  two  genera  Icosteus 
and  Icichthys  is  unossified,  and  is  perfectly  flexible. 
Approximations  to  this  state  of  things  are  seen  in  the 
parasitic  genus  Cyclopterus,  and  in  the  ribbon-fishes, 
Trachypteridae. 

Thus  nearly  all  the  main  lines  of  the  Acanthopte- 
rygii  are  degenerate  ;  the  exceptions  are  those  that 
terminate  in  the  Scombridae  (mackerel),  Serranidae, 
and  Scaridae  (Pharyngognathi). 

c.    The  Line  of  the  Batrachia. 

We  know  Batrachia  first  in  the  Coal  Measures. 
They  reach  a  great  development  in  the  Permian  epoch, 
and  are  represented  by  large  species  in  the  Triassic 


PHYLOGENY.  109 

period.  From  that  time  they  diminish  in  numbers, 
and  at  the  present  day  form  an  insignificant  part  of 
the  vertebrate  fauna  of  the  earth.  The  history  of  their 
succession  is  told  by  a  table  of  classification  such  as  I 
give  below : 

I.  Supraoccipital,  tabular,  and  supramastoid  bones  present.     Pro- 
podial  bones  distinct.  STEGOCEPHALI. 

Vertebral  centra,  including  atlas,  segmented,  one  set  of 
segments  together  supporting  one  arch  ;  Rhachitomi. 

Vertebrae  segmented,  the  superior  and  inferior  segments 
each  complete,  forming  two  centra  to  each  arch ; 

Embolomeri. 

Vertebral  centra,  including  atlas,  not  segmented,  one  to 
each  arch;  Microsauri. 

II.  Supraoccipital  and  supramastoid  bones  wanting.     Frontal  and 
propodial  bones  distinct ;  URODELA. 

a.  An  os  tabulare. 

A  palatine  arch  and  separate  caudal  vertebras  ;  Proteida 
aa.   No  os  tabulare. 

A  maxillary  arch  ;  palatine  arch  imperfect ;  nasals,  pre- 
maxillaries  and  caudal  vertebrae  distinct ; 

Pseudosauria.1 

'    No  maxillary  or  palatine  arches  ;  nasals  and  premaxil- 
liary,  also  caudal  vertebrae,  distinct ;    Trachystomata. 

III.  Supraoccipital,    tabular,    and   supramastoid   bones  wanting. 
Frontals  and  parietals  connate  ;  propodial  bones  and  caudal 
vertebrae  confluent ;  SALIENTIA. 

Premaxillaries  distinct  from  nasals  ;  no  palatine  arch  ; 
astragalus  and  calcaneum  elongate,  forming  a  distinct 
segment  of  the  limb  ;  Anura. 

The  probable  phylogeny  of  these  orders  as  imper- 
fectly indicated  by  paleontology  is  exhibited  in  the 
diagram  on  the  following  page. 

An  examination  of  the  above  tables  shows  that 
there  has  been  in  the  history  of  the  batrachian  class  a 
reduction  in  the  number  of  the  elements  composing 

1  Includes  the  Gymnophiona. 


no    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

the  skull,  both  by  loss  and  by  fusion  with  each  other. 
It  also  shows  that  the  vertebrae  have  passed  from  a 
notochordal  state  with  segmented  centra,  to  biconcave 
centra,  and  finally  to  ball-and-socket  centra,  with  a 
great  reduction  of  numbers.  It  is  also  the  fact  that 
the  earlier  forms  (those  of  the  Permian  epoch)  show 
the  most  mammalian  characters  of  the  tarsus  and  of 
the  pelvis.  The  later  forms,  the  salamanders,  show  a 
more  generalized  form  of  carpus  and  tarsus  and  of 
pelvis  also.  In  the  latest  forms,  the  Anura,  the  carpus 
and  tarsus  are  reduced  through  loss  of  parts,  except 


Salientia 


Traphystomata 


that  the  astragalus  and  calcaneum  are  phenomenally 
elongate.  We  have  then,  in  the  batrachian  series,  a 
somewhat  mixed  kind  of  change  ;  but  it  principally 
consists  of  concentration  and  consolidation  of  parts. 
The  question  as  to  whether  this  process  is  one  of  pro- 
gression or  retrogression  may  be  answered  as  follows  • 
If  degeneracy  consists  in  "the  loss  of  parts  without 
complementary  addition  of  other  parts,"  then  the  ba- 
trachian line  is  a  degenerate  line.  This  is  only  partly 
true  of  the  vertebral  column,  which  presents  the  most 
primitive  characters  in  the  early,  Permian,  genera 
(Rhachitomi).  If  departure  from  the  nearest  approx- 


PHYLOGENY. 


in 


imation  to  the  Mammalia  is  degeneracy,  then  the 
changes  in  this  class  come  partly  under  that  head.  The 
scapular  and  pelvic  arches  of  the  Rachitomi  are  more 
mammalian  than  are  those  of  any  of  their  successors  ; 


Fig.  27. — Cricotus  crassidiscus  Cope,  parts  of  individual  represented  in 
Fig.  28;  one-third  natural  size.  From  Permian  of  Texas,  a,  head  from  above; 
b,  part  of  belly  from  below.  From  Cope. 

the   carpus   and   tarsus   are  less  so   than  that  of  the 
Anura. 

There  are  several  groups  which  show  special  marks 
of  degeneracy.      Such  are  the  reduced  maxillary  bones 


PHYLOGENY.  113 

and  persistent  gills  of  the  Protei'da ;  the  absence  of 
the  maxillary  bones  and  the  presence  of  gills  in  the 
Trachystomata  ;  the  loss  of  a  pair  of  legs  and  feeble- 
ness of  the  remaining  pair  in  the  same  ;  and  the  ex- 
treme reduction  of  the  limbs  in  Amphiuma,  and  their 
total  loss  in  the  Caeciliidae.  Such  I  must  also  regard, 
with  Lankester,  the  persistent  branchiae  of  the  sire- 
dons.  I  may  add  that  in  the  brain  of  the  protei'd  Nec- 
turus  the  hemispheres  are  relatively  larger  than  in  the 
Anura,  which  are  at  the  end  of  the  line. 

It  must  be  concluded,  then,  that  in  many  respects 
the  Batrachia  have  undergone  degeneracy  with  the 
passage  of  time. 

d.    The  Reptilian  Line. 

As  in  the  case  of  the  Batrachia,  the  easiest  way  of 
obtaining  a  general  view  of  the  history  of  this  class  is 
by  throwing  their  principal  structural  characters  into  a 
tabular  form.  As  in  the  case  of  that  class,  I  commence 
with  the  oldest  forms  and  end  with  the  latest  in  the 
order  of  time,  which,  as  usual,  corresponds,  with  the 
order  of  structure.  I  except  from  this  the  first  order, 
the  Ichthyopterygia,  which  we  do  not  know  prior  to 
the  Triassic  period  : 

I.  The  quadrate  bone  united  with  the  adjacent  elements  by  suture. 
A.    Temporal  region  of  skull  with  a  bony  roof  ;  no  postorbital 
bars. 

Supramastoid   bone   present ;    an   interclavicle ;    limbs 

ambulatory ;  Cotylosauria. 

AA.  Cranium  with  one  postorbital  bar ;  no  sternum.     (Sy- 

naptosauria.) 
a.  Paroccipital  bone  distinct. 

A  supramastoid  bone ;  ribs  two-headed  on  centrum ; 
carpals  and  tarsals  not  distinct  in  form  from  meta- 
podials ;  Ichthyopterygia. 


ii4    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

No  supramastoid  ;  sub-  and  postpelvic  ossifications ;  in- 

terclavicle  and  clavicles  separated  from  and  below 

scapular  arch  ;  ribs  one-headed  on  centrum  ;  coracoid 

large,  free  posteriorly  ;  Testudinata. 

aa.  Paroccipital  bone  not  distinct. 

Ribs  one  or  two-headed,  capitulum  intercentral ;  clav- 
icles and  interclavicles  forming  part  of  shoulder- 
girdle  ;  scapula  simple  ;  pubis  and  ischium  plate-like 
with  small  or  no  obturator  foramen  ;  no  sub-  or 
post-pelvic  bones  ;  no  supramastoid  ;  Theromora. 
Supramastoid  present ;  ribs  one-headed  ;  scapula  trira- 
diate  ;  no  sternum  ;  pubis  and  ischium  plate-like ;  no 
sub-  or  postpelvic  bones  ;  Plesiosauria. 

AAA.  Cranium  with  two  postorbital  bars  ;  a  sternum.  (Archo- 
sauria. ) 
Paroccipital  bone  not  distinct ;  no  supramastoid. 

Ribs   two-headed  ;  no   interclavicle ;  external   anterior 
digits  greatly  elongate  to  support  a  patagium  ; 

Ornithosauria. 

Ribs  two-headed ;    no  interclavicle ;    acetabulum  per- 
forate ;  limbs  ambulatory  ;  Dinosauria. 
Ribs  two-headed  ;  an  interclavicle  ;  acetabulum  closed  ; 
feet  ambulatory  ;  Crocodilia. 
Ribs  one  headed  ;  an  interclavicle  ;  acetabulum  closed  ; 
feet  ambulatory  ;                                   Rhynchocephalia. 
II.  The  quadrate  loosely  articulated  with  the  adjacent  elements, 
and  only  proximally.     (Streptostylica. ) 

One  postorbital  bar,  when  present ;  a  paroccipital ;  su- 
pramastoid not  distinct ;  ribs  one-headed;  Squamata. 

An  inspection  of  the  characters  of  these  ten  orders, 
and  their  consideration  in  connection  with  their  geo- 
logical history,  will  give  a  definite  idea  as  to  the  char- 
acter of  their  evolution.  The  history  of  the  class,  and 
therefore  the  discussion  of  the  question,  is  limited  in 
time  to  the  period  which  has  elapsed  since  the  Per- 
mian epoch  inclusive,  for  it  is  then  that  the  Reptilia 
enter  the  field  of  our  knowledge.  During  this  period 
two  remarkable  orders  of  reptiles  inhabited  the  earth, 


PHYLOGENY. 


those  of  the  Cotylosauria  and  of  the  Theromora.  The 
important  character  and  role  of  these  types  may  be 
inferred  from  the  fact  that  the  Cotylosauria  are  struc- 
turally nearer  to  the  Batrachia  and  the  Theromora  to 
the  Mammalia  than  any  other,  and  the  former  presents 
characters  which  render  it  probable  that  all  the  other 
reptiles  derived  their  being  from  them.  The  phylogeny 
may  be  thus  expressed  : 

MAMMALIA 
Pterosauria 

Dinosauria 

Crocodilia 

X 


Squamata ! 


Icbth 


Sauropterygia 

Anomodonta 

Testudinata 


ylosauri; 


It  is  extremely  probable  that  the  characters  of  the 
posterior  parts  of  the  cranium  of  reptiles,  as  seen  in 
the  osseous  bars  posterior  to  the  orbit,  were  derived 
by  a  kind  of  natural  trephining  of  the  cranial  roof  of 
the  primitive  order  of  the  Cotylosauria.  This  order 
has  left  remains  in  the  Permian  beds  of  North  Amer- 
ica, South  Africa,  and  Germany.  This  is  the  theory 
of  Baur,3and  I  have  rendered  it  probable  by  researches 
on  the  Permian  genera  of  North  America.4 

1  Some  unknown  type  of  Pythonomorpha  will  represent  the  ancestor  of 
the  Ophidia,  while  it  is  uncertain  whether  this  order  originated  from  the 
Theriodonta  or  the  Rhynchocephalia. 

2  The  Theromora  include  the  Pelycosauria,  Theriodonta,    Anomodonta, 
and  other  suborders. 

3  American  Journal  of  Morphology ,  1889,  p.  471. 

4  Trans.  Amer.  Philos.   Society,  1892,  p.  13  ;  American  Naturalist,  1892,  p. 
407. 


n6    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

The  diagrams  on  pages  117-119  illustrate  the  suc- 
cessive changes  in  the  structure  of  the  posterior  region 
of  the  skull  in  the  types  mentioned.  The  orders  and 
suborders  Pseudosuchia,  Rhynchocephalia,  Ichthyo- 
pterygia,  Dinosauria,  Crocodilia,  Sauropterygia,  and 
Testudinata  commence  at  the  beginning  of  Mesozoic 
time,  after  the  Permian  had  closed.  The  Squamata 
(lizards  and  snakes)  commence,  so  far  as  is  certainly 
known,  in  the  later  Mesozoic,  in  the  Cretaceous  period. 

The  line  which  terminated  in  the  Lacertilia  and 
Ophidia  (Squamata)  may  have  originated  directly  from 
the  Theriodonta,  or  it  may  have  descended  from  the 
Rhynchocephalia.  It  departs  from  the  former  type  in 
two  respects  : 

First,  in  the  loss  of  the  capitular  articulation  of  the 
ribs,  and,  second,  in  the  gradual  elongation  and  final 
freedom  of  the  suspensory  bone  of  the  lower  jaw  (the 
os  quadratum).  In  so  departing  from  the  Theromora, 
it  also  departs  from  the  mammalian  type.  The  ribs 
assume  the  less  perfect  kind  of  attachment  which  the 
mammals  only  exhibit  in  some  of  the  whales,  and  the 
articulation  of  the  lower  jaw  loses  in  strength,  while 
it  gains  in  extensibility,  as  is  seen  in  the  develop- 
ment of  the  line  of  the  eels  among  fishes.  The  end 
of  this  series,  the  snakes,  must  therefore  be  said  to  be 
the  result  of  a  process  of  creation  by  degeneration,  and 
their  lack  of  scapular  arch  and  fore  limb  and  usual 
lack  of  pelvic  arch  and  hind  limb  are  confirmatory 
evidence  of  the  truth  of  this  view  of  the  case. 

Secondly,  as  regards  the  ossification  of  the  anterior 
part  of  the  brain-case.  This  is  deficient  in  some  of 
the  Theromora,  the  ancestral  series,  which  resemble  in 
this,  as  in  many  other  things,  the  contemporary  Ba- 
trachia.  The  late  orders  mostly  have  the  anterior  walls 


PHYLOGENY. 


117 


n8  PRIMARV  FACTORS  OF  ORGANIC  EVOLUTION. 


PHYLOGENY. 


119 


120    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

membranous,  but,  in  the  streptostylicate  series  at  the 
end,  the  skull  in  the  snakes  becomes  entirely  closed  in 
front.  In  this  respect,  then,  the  latter  may  be  said  to 
be  the  highest  or  most  perfect  order. 

As  regards  the  scapular  arch,  including  the  ster- 
num, no  order  possesses  as  many  elements  as  thor- 
oughly articulated  for  the  use  of  the  anterior  leg  as  the 
Permian  Theromora  (excepting  in  the  suborder  Pelyco- 
sauria).  In  all  the  orders  there  is  loss  of  parts,  except- 
ing only  in  the  Ornithosauria  and  the  Lacertilia.  In 
the  former  the  adaptation  is  to  flying.  The  latter  re- 
tain nearly  the  theromorous  type.  An  especial  side 
development  is  the  modification  of  abdominal  bones 
into  three  pairs  of  peculiar  elements  to  be  united  with 
part  of  the  scapular  arch  into  a  plastron,  and  the  in- 
clusion of  the  coracoid  above  them,  seen  in  the  Testu- 
dinata. 

The  pelvic  arch  has  a  more  simple  history.  Again, 
in  the  Theromora  we  have  the  nearest  approach  to  the 
Mammalia.  The  only  other  order  which  displays  sim- 
ilar characters  is  the  Ornithosauria  (Dimorphodon, 
according  to  Seeley).  In  the  Dinosauria  we  have  a 
side  modification  which  is  an  adaptation  to  the  erect 
or  bipedal  mode  of  progression,  the  inferior  bones  be- 
ing thrown  backward  so  as  to  support  the  viscera  in  a 
more  posterior  position  in  birds.  This  is  an  obvious 
necessity  to  a  bipedal  animal  where  the  vertebral  col- 
umn is  not  perpendicular.  And  it  is  from  the  Triassic 
Dinosauria  that  I  suppose  the  birds  to  have  arisen.  The 
main  line  of  the  Reptilia,  however,  departs  from  both 
the  mammalian  and  the  avian  type  and  loses  in  strength 
as  compared  with  the  former.  In  the  latest  orders, 
the  Pythonomorpha  and  Ophidia,  the  pelvis  is  rudi- 
mental  or  absent. 


PHYLOGENY.  121 

As  regards  the  limbs,  the  degeneracy  is  well  marked. 
No  reptilian  order  of  later  ages  approaches  so  near  to 
the  Mammalia  in  these  parts  as  do  the  Permian  Thero- 
mora.  This  approximation  is  seen  in  the  internal  epi- 
condylar  foramen  and  well-developed  condyles  of  the 
humerus,  and  in  the  well-differentiated  seven  bones  of 
the  tarsus.  The  epicondylar  foramen  is  only  retained 
in  later  reptiles  in  the  rhynchocephalian  Sphenodon 
(Dollo);  and  the  condyles  of  the  Dinosauria  and  all  of 
the  other  orders,  excepting  the  Ornithosauria  and  some 
Lacertilia,  are  greatly  wanting  in  the  strong  charac- 
terization seen  in  the  Theromora.  The  posterior  foot 
seems  to  have  stamped  out  the  greater  part  of  the  tar- 
sus in  the  huge  Dinosauria,  and  it  is  reduced,  though 
to  a  less  degree,  in  all  the  other  orders.  In  the  paddled 
Plesiosauria,  dwellers  in  the  sea,  the  tarsus  and  carpus 
have  lost  all  characterization,  probably  by  a  process  of 
degeneracy,  as  in  the  mammalian  whales.  This  is  to 
be  inferred  from  the  comparatively  late  period  of  their 
appearance  in  time.  The  still  more  unspecialized  feet 
and  limbs  of  the  Ichthyosaurus  (Ichthyopterygia)  can 
not  yet  be  ascribed  to  degeneracy,  for  their  history  is 
too  little  known.  At  the  end  of  the  line,  the  snakes 
present  us  with  another  evidence  of  degeneracy.  But 
few  have  a  pelvic  arch  (Glauconiidae  Peters),  while 
very  few  (Peropoda)  have  any  trace  of  a  posterior 
limb. 

The  vertebrae  are  not  introduced  into  the  definitions 
of  the  orders,  since  they  are  not  so  exclusively  distinc- 
tive as  many  other  parts  of  the  skeleton.  They  never- 
theless must  not  be  overlooked.  As  in  the  Batrachia, 
the  Permian  orders  show  inferiority  in  the  deficient 
ossification  of  the  centrum.  Many  of  the  Theromora 
are  notochordal,  a  character  not  found  in  any  later  or- 


122    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

der  of  reptiles  excepting  in  a  few  Lacertilia  (Gecconi- 
dae).  They  thus  differ  from  the  Mammalia,  whose 
characters  are  approached  more  nearly  by  some  of  the 
terrestrial  Dinosauria  in  this  respect.  Leaving  this 
order,  we  soon  reach  the  prevalant  ball-and-socket 
type  of  the  majority  of  Reptilia.  This  strong  kind  of 
articulation  is  a  need  which  accompanies  the  more 
elongated  column  which  itself  results  at  first  from  the 
posterior  direction  of  the  ilium.  In  the  order  with  the 
longest  columrt,  the  Ophidia,  a  second  articulation, 
the  zygosphen,  is  introduced.  The  mechanical  value 
of  the  later  reptilian  vertebral  structure  is  obvious,  and 
in  this  respect  the  class  may  be  said  to  present  a  higher 
or  more  perfect  condition  than  the  Mammalia. 

In  review  it  may  be  said  of  the  reptilian  line,  that 
it  exhibits  marked  degeneracy  in  its  skeletal  structure 
since  the  Permian  epoch  ;  the  exception  to  this  state- 
ment being  in  the  nature  of  the  articulations  of  the 
vertebra?.  And  this  specialization  is  an  adaptation  to 
one  of  the  conditions  of  degeneracy,  viz.,  the  weaken- 
ing and  final  loss  of  the  limbs  and  the  arches  to  which 
they  are  attached. 

The  history  of  the  development  of  the  brain  in  the 
Reptilia  presents  some  interesting  facts.  In  the  dia- 
dectid  family  of  the  Permian  Cotylosauria  it  is  smaller 
than  in  a  Boa  constrictor,  but  larger  than  in  some  of 
the  Jurassic  Dinosauria.  Marsh  has  shown  that  some 
of  the  latter  possess  brains  with  relatively  very  narrow 
hemispheres,  so  that  in  this  organ  those  gigantic  rep- 
tiles were  degenerate,  while  the  existing  streptostyli- 
cate  orders  have  advanced  beyond  their  Permian  an- 
cestors. 

There  are  many  remarkable  cases  of  what  may  now 
be  safely  called  degradation  to  be  seen  in  the  contents 


PHYLOGENY.  123 

of  the  orders  of  reptiles.1  Among  tortoises  may  be 
cited  the  loss  of  one  or  two  series  of  phalanges  in  sev- 
eral especially  terrestrial  families  of  the  Testudinidae. 
The  cases  among  the  Lacertilia  are  the  most  remark- 
able. The  entire  families  of  the  Pygopodidae,  the 
Anniellidae,  the  Anelytropidae,  and  the  Dibamidae  are 
degraded  from  superior  forms.  In  the  Anguidae,  Te- 
idae,  and  Scincidae,  we  have  series  of  forms  whose  steps 
are  measured  by  the  loss  of  a  pair  of  limbs,  or  of  from 
one  to  all  the  digits,  and  even  to  all  the  limbs.  In 
some  series  the  surangular  bone  is  lost.  In  others  the 
eye  diminishes  in  size,  loses  its  lids,  loses  the  folds 
of  the  epidermis  which  distinguish  the  cornea,  and 
finally  is  entirely  obscured  by  the  closure  of  the  oph- 
thalmic orifice  in  the  true  skin.2  Among  the  snakes 
a  similar  degradation  of  the  organs  of  sight  has  taken 
place  in  two  suborders,  which  live  underground,  and 
often  in  ants'  nests.  The  Tortricidae  and  Uropeltidae 
are  burrowing-snakes  which  display  some  of  the  earlier 
stages  of  this  process.  One  genus  of  the  true  colubrine 
snakes  even  (according  to  Gunther)  has  the  eyes  ob- 
scured as  completely  as  those  of  the  inferior  types 
above  named  (genus  Typhlogeophis.) 

e.    The  Avian  Line. 

The  paleontology  of  the  birds  not  being  well  known, 
our  conclusions  respecting  the  character  of  their  evo- 
lution must  be  very  incomplete.  A  few  lines  of  suc- 
cession are,  however,  quite  obvious,  and  some  of  them 
are  clearly  lines  of  progress,  and  others  are  lines  of  re- 

1  Such  forms  in  the  Lacertilia  have  been  regarded  as  degradational  by 
Lankester  and  Boulanger. 

2A  table  of  the  degenerate  forms  of  Lacertilia  is  given  in  the  chapter  on 
Catagenesis. 


124    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

trogression.  The  first  bird  we  know  at  all  completely, 
is  the  celebrated  Archeopteryx  of  the  Solenhofen  slates 
of  the  Jurassic  period.  In  its  elongate  series  of  caudal 
vertebrae  and  the  persistent  digits  of  the  anterior  limbs 
we  have  a  clear  indication  of  the  process  of  change 
which  has  produced  the  true  birds,  and  we  can  see 
that  it  involves  a  specialization  of  a  very  pronounced 
sort.  The  later  forms  described  by  Seeley  and  Marsh 
from  the  Cretaceous  beds  of  England  and  North  Amer- 
ica, some  of  which  have  biconcave  vertebras,  and  all 
probably,  the  American  forms  certainly,  possessed 
teeth.  This  latter  character  was  evidently  speedily 
lost,  and  others  more  characteristic  of  the  subclass  be- 
came the  field  of  developmental  change.  The  parts 
which  subsequently  attained  especial  development  are 
the  wings  and  their  appendages ;  the  feet  and  their 
envelopes,  and  the  vocal  organs.  Taking  all  things 
into  consideration,  the  greatest  sum  of  progress  has 
been  made  by  the  perching  birds,  whose  feet  have  be- 
come effective  organs  for  grasping,  whose  vocal  organs 
are  most  perfect,  and  whose  flight  is  generally  good, 
and  often  very  good.  In  these  birds  also  the  circula- 
tory system  is  most  modified,  in  the  loss  of  one  of  the 
carotid  arteries. 

The  power  of  flight,  the  especially  avian  charac- 
ter, has  been  developed  most  irregularly,  as  it  appears 
in  all  the  orders  in  especial  cases.  This  is  apparent 
so  early  as  in  the  Cretaceous  toothed  birds  already 
mentioned.  According  to  Marsh,  the  Hesperornithidae 
have  rudimental  wings,  while  these  organs  are  well 
developed  in  the  Ichthyornithidae.  They  are  well  de- 
veloped among  natatorial  forms  in  the  albatrosses  and 
frigate  pelicans,  and  in  the  skuas,  gulls,  and  terns, 
and  are  rudimental  in  their  allies,  the  auks.  They  are 


PHYLOGENY. 


125 


developed   among   rasorial  types  in  the  sand-grouse, 
and,  among  the  adjacent  forms,  the  pigeons.      Then 


w  x 


Fig.  32. — Archteopteryx  lithographica, 
from  the  middle  Oolite  of  Bavaria. 


among  the  lower  Passeres,  the  humming-birds  exceed 
all  birds  in  their  powers  of  flight,  and  the  swifts  and 


126    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

some  of  the  Caprimulgidae  are  highly  developed  in  this 
respect.  Among  the  higher  or  true  song  birds,  the 
swallows  form  a  notable  example.  With  these  high 
specializations  occur  some  remarkable  deficiencies. 
Such  are  the  reduction  of  the  feet  in  the  Caprimulgidae, 
swifts,  and  swallows,  and  the  foetal  character  of  the 
bill  in  the  same  families.  In  the  syndactyle  families, 
represented  by  the  kingfishers,  the  condition  of  the 
feet  is  evidently  the  result  of  a  process  of  degenera- 
tion. 

A  great  many  significant  points  may  be  observed 
in  the  developmental  history  of  the  epidermic  struc- 
tures, especially  in  the  feathers.  The  scale  of  change 
in  this  respect  is  in  general  a  rising  one,  though  vari- 
ous kinds  of  exceptions  and  variations  occur.  In  the 
development  of  the  reetrices  (tail-feathers)  there  are 
genera  of  the  wading  and  rasorial  types,  and  even  in 
the  insessorial  series,  where  those  feathers  are  of  prim- 
itive structure  (Menuridae),  are  greatly  reduced,  or 
absolutely  wanting.  These  are  cases  of  degeneracy. 

There  is  no  doubt  that  the  avian  series  is  in  gen- 
eral an  ascending  one. 

f.    The  Mammalian  Line. 

Discoveries  in  paleontology  have  so  far  invalidated 
the  accepted  definitions  of  the  orders  of  this  class  that 
it  is  difficult  to  give  a  clearly  cut  analysis,  especially 
from  the  skeleton  alone.  The  following  scheme,  there- 
fore, while  it  expresses  the  natural  groupings  and  affin- 
ities, is  defective,  in  that  some  of  the  definitions  are 
not  without  exceptions  : * 

IThis  classification  of  the  Mammalia  was  first  published  by  the  writer 
in  the  American  Naturalist  for  1885  ;  was  improved  in  the  same,  1889  (October;; 
and  appeared  in  a  Syllabus  of  Lectures  of  the  University  of  Pennsylvania, 
July,  1891. 


PHYLOGENY.  127 

I.  A  large  coracoid  bone  articulating  with  the  sternum.     An  inter- 
clavicle  (Prototheria). 

Epicoracoid  and  marsupial  bones  ;  fibula  articulating 
with  proximal  end  of  astragalus  :       i.  Monotremata. 

II.  Coracoid  a  small  process  coossified  with  the  scapula  (Eutheria). 

a.  Marsupial  bones ;  palate  with  perforations  (uterus  divided  ; 
placenta  and  corpus  callosum  rudimental  or  wanting  ;  cere- 
bral hemispheres  small  and  generally  smooth). 

But  one  deciduous  molar  tooth  :  2.  Marsupialia 

aa.   No  marsupial  bones  ;  palate  generally  entire  (placenta  and 

corpus  callosum  well  developed). 

j8.  Anterior  limb  reduced  to  more  or  less  inflexible  paddles 
posterior  limbs  wanting  (Mutilata). 

Elbow-joint  fixed  ;  carpals  discoid,  and  with  the  digits 

separated  by  cartilage  ;  lower  jaw  without  ascending 

ramus  :  3.  Cetacea. 

Elbow-joint  flexible ;  carpals  and  phalanges  with  normal 

articulations  ;  lower  jaw  with  ascending  ramus  : 

4.  Sirenia. 
,3(3.  Anterior  limbs  with  flexible  joints.     Ungual  phalanges 

compressed  and  pointed1  (Unguiculata). 
; .   Feet  taxeopodous  (with  exceptions  in  the  carpus), 
d.   Teeth  without  enamel  ;  generally  no  incisors. 

Limbs  not  volant ;  hemispheres  small,  smooth  : 

5.  Edentata 
66.  Teeth  with  enamel ;  incisors  generally  present. 

No  postglenoid  process  ;  mandibular  condyle  not  trans- 
verse ;  limbs  not  volant  ;  hemispheres  small,  smooth  : 

6.  Glires 
Anterior  limbs  volant  ;  hemispheres  small,  smooth  : 

7.  Chiroptera 

A  postglenoid  process ;  mandibular  condyle  transverse  ; 
limbs  not   volant  ;    no   scapholunar   bone2;    hemi- 
spheres small,  smooth  :  8.  Bunotheria? 
A  postglenoid  process  ;  limbs  not  volant,  with  a  scapho- 
lunar bone  ;  hemispheres  larger,  convoluted  : 

9.  Carnivora. 

1  Except  Mesonychiidae. 

2  Except  Erinaceus  and  Talpa. 

3  With  the  suborders  Pantotheria,  Creodonta,  Insectivora,  and  Tillodonta 


128    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

yy.  Feet  diplarthrous. 

Limbs  ambulatory;  a  postglenoid  process  ;  molars  qua- 

dri tubercular :  10.  Ancylopoda. 

PPfl.  Anterior  limbs  with  flexible  joints  and  distinct  digits ; 

ungual  phalanges  not  compressed  and  acute  at  apex l  (Un- 

gulata2). 

e.  Tarsal  bones  in  linear  series ;  carpals  generally  in  linear 
series. 

Limbs  ambulatory;  teeth  with  enamel :  n.  Taxeopoda? 
££.  Carpal  series  alternating  ;  tarsal  series  linear. 

Limbs  ambulatory  ;  median  digits  longest ;  teeth  with 
enamel :  12.  Toxodontia. 

£E£.  Tarsal  series  alternating  ;  carpals  linear. 

Cuboid  bone  partly  supporting  navicular,  not  in  contact 
with  astragalus  :  13.  Proboscidia. 

eeee.  Both  tarsal  and  carpal  series  more  or  less  alternating. 
Os  magnum  not   supporting  scaphoides;   cuboid  sup- 
porting astragalus  ;  superior  molars  tritubercular  : 

14.  Amblypoda. 

Os  magnum  supporting  scaphoides ;    superior  molars 
quadritubercular  :  4  15.  Diplarthra* 

1  Except  the  Hapalidae. 

2  Lamarck,  Zoologie  Philosophique,  1809. 

3  This  order  has  the  following  suborders  : 

Carpal  series  linear ;  no  intermedium ;  tibia  not  interlocking  with  astraga- 
lus ;  no  anapophyses ;  incisors  rooted  ;  hallux  not  opposable  : 

Condylarthra, 

Carpal  series  linear;   an  intermedium;   tibia  interlocking  with  astragalus; 
hallux  not  opposable  :  Hyracoidea. 

An  intermedium;  fibula  not  interlocking;  anapophyses;  hallux  opposable; 
incisors  growing  from  persistent  pulps  :  Daubentonioidea. 

An  intermedium;  fibula  not  interlocking;  anapophyses;  hallux  opposable; 
incisors  rooted  ;  carpus  generally  linear  :  Quadrumana. 

No    intermedium ;  6    nor    anapophyses  ;    carpal  rows  alternating ;    incisors 
rooted :  Anthropomorpha.1 

The  only  difference  between  the  Taxeopoda  and  the  Bunotheria  is  in  the 

unguliform  terminal  phalanges  of  the  former  as  compared  with  the  clawed  or 

unguiculate  form  in  the  latter.    The  marmosets  among  the  former  division 

are,  however,  furnished  with  typical  claws. 

4  Except  Trigonolestes. 

fi  This  order  includes  the  suborders  Perissodactyla  and  Artiodactyla.     It 
is  the  Ungulata  of  some  authors. 

6  Except  in  Simia  and  Hylobates. 

7  Includes  the  Anthropoid  apes  and  man. 


PHYLOGENY. 


129 


i3o  PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


PHYLOGENY. 


132    PRIMARY  FACTORS  CF  ORGANIC  EVOLUTION. 

The  characters  of  the  skeleton  of  the  order  Mono- 
tremata  show  that  it  is  nearest  of  kin  to  the  Reptilia,  and 
many  subordinate  characters,  especially  of  the  extrem- 
ities, point  to  the  Theromora  as  its  ancestral  source.1 
In  the  general  characters  the  Marsupialia  naturally 
follow  in  a  rising  scale,  as  proved  by  the  increasing 
perfection  of  the  reproductive  system.  The  Monodel- 
phia  follow  with  improvements  in  the  reproductive 
system  and  the  brain,  as  indicated  in  the  table  above 
given.  The  oldest  Monodelphia  were,  in  respect  to 
the  structure  of  the  brain,  much  like  the  Marsupialia, 
and  some  of  the  existing  orders  resemble  them  in  some 
parts  of  their  brain-structure.  Such  are  the  Condylar- 
thra  and  Amblypoda  of  extinct  groups,  and  the  Buno- 
theria,  Edentata,  Glires,  and  Chiroptera,  recent  and 
extinct.  The  characters  of  the  brains  of  Amblypoda 
and  some  Creodonta  are,  in  their  superficial  char- 
acters, even  inferior  to  existing  marsupials.  The  di- 
vided uterus  of  the  recent  forms  named,  also  gives 
them  the  position  next  to  the  Marsupialia.  In  the 
Carnivora,  Hyracoidea,  and  Proboscidia,  a  decided  ad- 
vance in  both  brain-structure  and  reproductive  system 
is  evident.  The  hemispheres  increase  in  size,  and  they 
become  convoluted.  A  uterus  is  formed,  and  the  testes 
become  external,  etc.  In  the  Quadrumana  and  An- 
thropomorpha  the  culmination  in  these  parts  of  the 
structure  is  reached,  excepting  only  that,  in  the  lack 
of  separation  of  the  genital  and  urinary  efferent  ducts, 
the  males  are  inferior  to  those  of  many  of  the  Artio- 
dactyla.  This  history  displays  a  rising  scale  for  the 
Mammalia.2 

1  Proceedings  American  Philosoph.  Society,  1884,  p.  43.     Antea,  p.  87. 

2  See  the  evidence  for  evolution  in  the  history  of  the  extinct  Mammalia 
Proceedings  of  the  American  Association  for  the  Advancement  of  Science,  1883. 


PHYLOGENY.  133 

Looking  at  the  skeleton,  we  observe  the  following 
successional  modifications  : 

First,  as  to  the  feet,  and  (A)  the  digits.  The  Con- 
dylarthra  have  five  digits  on  both  feet,  and  they  are 
plantigrade.  This  character  is  retained  in  their  de- 
scendants of  the  lines  of  Anthropomorpha,  Quadru- 
mana,  and  Hyracoidea,  also  in  the  Bunotheria,  Eden- 
tata, and  most  of  the  Glires.  In  some  of  the  Amblypoda 
and  in  the  Proboscidia  the  palm  and  heel  are  a  little 
raised.  In  the  Carnivora  and  Diplarthra  the  heel  is 
raised,  often  very  high,  above  the  ground,  and  the 
number  of  toes  is  diminished,  as  is  well  known,  to  two 
in  the  Artiodactyla  and  one  in  the  Perissodactyla. 

(B)  The  tarsus  and  carpus.      In  the  Condylarthra  and 
most  of  the  Creodonta  the  bones  of  the  two  series  in 
the  carpus  and  tarsus  are  opposite  each  other,  so  as  to 
form  continuous  and  separate   longitudinal   series  of 
bones.      This  continues  to  be  the  case  in  the  Hyracoi- 
dea and  many  of   the  Quadrumana,  but  in  the  anthro- 
poid apes  and  man  the  second  row  is  displaced  inwards 
so  as  to  alternate  with  the  first  row,  thus  interrupting 
the  series  in  the  longitudinal  direction,  and  forming  a 
stronger  structure  than  that  of   the  Condylarthra.      In 
the  bunotherian,  rodent,  and  edentate  series,  the  tar- 
sus continues  to  be  without  alternation,  as  in  the  Con- 
dylarthra, and  is  generally  identical  in  the  Carnivora. 
In  the  hoofed  series  proper  it  undergoes  change.      In 
the  Proboscidia  the  carpus  continues  linear,  while  the 
tarsus  alternates.      In  the  Amblypoda  the  tarsus  alter- 
nates in  another  fashion,  and  the  carpal  bones  are  on 
the  inner  side  linear,  and  on  the  outer  side  alternating. 
The  complete  interlocking  by  universal  alternation  of 
the  two  carpal  series  is  only  found  in  the  Diplarthra. 

(C)  As  to  the  ankle-joint.   In  most  of  the  Condylarthra 


PHYLOGENY.  135 

it  is  a  flat  joint  or  not  tongued  or  grooved.  In  most 
of  the  Carnivora,  in  a  few  Glires,  and  in  all  Diplar- 
thra,  it  is  deeply  tongued  and  grooved,  forming  a  more 
perfect  and  stronger  joint  than  in  the  other  orders, 
where  the  surfaces  of  the  tibia  and  astragalus  are  flat. 
(D)  In  the  highest  forms  of  the  Rodentia  and  Diplar- 
thra  the  fibula  and  ulna  become  more  or  less  coossified 
with  the  tibia  and  radius,  and  their  middle  portions 
become  attenuated  or  disappear. 

Secondly,  as  regards  the  vertebrae.  The  mutual 
articulations  (zygapophyses)  in  the  Condylarthra  have 
flat  and  nearly  horizontal  surfaces.  In  higher  forms, 
especially  of  the  ungulate  series,  they  become  curved, 
the  posterior  turning  upward  and  outward,  and  the  an- 
terior embracing  them  on  the  external  side.  In  the 
higher  Diplarthra  this  curvature  is  followed  by  another 
curvature  of  the  postzygapophysis  upward  and  out- 
ward, so  that  the  vertical  section  of  the  face  of  this 
process  is  an  S.  Thus  is  formed  a  very  close  and  se- 
cure joint,  such  as  is  nowhere  seen  in  any  other  Verte- 
brata. 

Thirdly,  as  regards  the  dentition.  Of  the  two  types 
of  Monotremata,  the  Tachyglossus,  and  the  Platy- 
pus, the  known  genera  of  the  former  possess  no  teeth, 
and  the  known  genus  of  the  latter  possesses  only  a 
single  corneous  epidermic  grinder  succeeding  two  de- 
ciduous molars,  like  those  of  certain  extinct  forms,  in 
each  jaw.  As  the  theromorous  reptiles  from  which 
these  are  descended  have  well-developed  teeth,  their 
condition  is  evidently  one  of  degeneration.  We  prob- 
ably have  their  ancestors  in  the  Multituberculata, 
which  range  from  Triassic  to  lower  Eocene  time  in 
both  hemispheres.  In  the  marsupial  order  we  have  a 
great  range  of  dental  structure,  which  almost  epito- 


136    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

mizes  that  of  the  monodelph  orders.  The  dentition 
of  the  carnivorous  forms  is  creodont ;  that  of  the  kan- 
garoos is  perissodactyle,  and  that  of  the  wombats  is 
rodent.  Other  forms  repeat  the  Insectivora.  I  there- 
fore consider  the  placental  series  especially.  I  have 
already  shown  that  the  greater  number  of  the  types  of 
this  series  have  derived  the  characters  of  their  molar 
teeth  from  the  stages  of  the  following  succession. 
First,  a  simple  cone  or  reptilian  crown,  alternating 
with  that  of  the  other  jaw.  Second,  a  cone  with  an- 
terior and  posterior  lateral  denticles.  Third,  the  den- 
ticles rotated  to  the  inner  side  of  the  crown  below,  and 
outer  side  above  forming  with  the  principal  (median) 
cone  a  three-sided  prism,  with  tritubercular  apex, 
which  alternates  with  that  of  the  opposite  jaw.  Fourth, 
development  of  a  heel  projecting  from  the  posterior 
base  of  the  lower  jaw,  which,  in  mastication,  meets 
the  crown  of  the  superior,  forming  a  tubercular-sec- 
torial  inferior  molar.  From  this  stage  the  carnivorous 
and  sectorial  dentition  is  derived,  the  tritubercular 
type  being  retained.  Fifth,  the  development  of  a  pos- 
terior inner  cusp  in  the  superior  molar,  and  the  eleva- 
tion of  the  heel  in  the  inferior  molar,  with  the  loss  of 
the  anterior  inner  cusp.  Thus  the  molars  become  qua- 
dritubercular,  and  opposite.  This  is  the  type  of  many 
of  the  Taxeopoda,  including  the  Quadrumana  and  In- 
sectivora as  well  as  the  inferior  Diplarthra.  The  higher 
Taxeopoda  (Hyracoidea)  and  Diplarthra  add  various 
complexities.  Thus  the  tubercles  become  flattened 
and  then  concave,  so  as  to  form  V's  in  the  section  pro- 
duced by  wearing  ;  or  they  are  joined  by  cross-folds, 
forming  various  patterns,  of  which  the  most  special- 
ized is  that  of  the  horse.  In  the  Proboscidia  the  latter 


PHYLOGENY. 


137 


Fig-  37-— A  Phenacodus  primervus,  fore  and  hind  limbs  ;  B,  Homo  sapiens, 
fore  and  hind  limbs. 


1 38     PR  I  MAR  Y  FA  CTORS  OF  OR  GANIC  E  VOL  UTION. 

become  multiplied  so  as  to  produce  numerous  cross- 
crests.   . 

The  molars  of  some  of  the  Sirenia  are  like  that  of 
some  of  the  Ungulata,  especially  of  the  tapirine  group, 
while  in  others  the  teeth  consist  of  cylinders.  In  the 
Cetacea  the  molars  of  the  oldest  (Eocene  and  Miocene) 
types  are  but  two-rooted  and  compressed,  having  much 
the  form  of  the  premolars  of  other  Mammalia.  In  ex- 
isting forms  a  few  have  simple  conical  teeth,  while  in 
a  considerable  number  teeth  are  entirely  wanting. 

g.    General  Review  of  the  Phytogeny  of  Mammalia. 

In  the  accompanying  table  some  of  the  characters 
of  the  mammalian  skeleton  above  described  are  thrown 
into  a  tabular  form.  They  are  exhibited  in  the  order 
of  their  appearance  in  geological  time,  beginning  with 
the  oldest  horizon  at  the  bottom  of  the  left-hand  col- 
umn. Continued  primitive  types  are  enclosed  in  brack- 
ets. These  relations  were  pointed  out  by  me  in  1883, ! 
and  every  discovery  made  since  that  date  has  confirmed 
their  correctness.  Some  characters  of  the  Mesozoic 
Mammalia  are  now  added. 

Paleontology  has  cleared  up  the  phylogeny  of  most 
of  the  mammalian  orders,  but  some  of  them  remain  as 
yet  unexplained.  This  is  the  case  with  the  Cetacea, 
the  Sirenia,  and  the  Edentata.  The  Marsupialia  can 
be  supposed  with  much  probability  to  have  come  off 
from  the  Monotremata,  but  there  is  but  little  paleon- 
tological  evidence  to  sustain  the  hypothesis.  Little 
progress  has  been  made  in  unravelling  the  phylogeny 

1  Proceedings  American  Assoc.  Adv.  Science,  p.  40.  The  successional  gra- 
dation in  the  limbs  and  teeth  was  announced  by  me  in  1873  (Proceeds.  Acad- 
emy Philadelphia,  p.  371,  and  Journal  of 'the  Academy,  1874,  p.  20),  and  that  in 
the  size  of  the  hemispheres  of  the  brain  by  Marsh  in  1874  (American  Journal 
Sci.  Arts,  p.  66). 


PHYLOGENY. 


139 


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r4o    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

of  the  Cetacea  and  Sirenia.  The  results  attained  by 
the  study  of  the  paleontology  of  the  other  orders  may 
be  summarized  as  follows  : 

First.  It  is  probable  that  the  common  ancestors  of 
the  placental  and  implacental  lines  of  Mammalia  are 
known  to  us  in  some  of  the  types  of  the  Jurassic  per- 
iod. Whether  they  were  marsupial  in  the  sense  of 
possessing  an  external  pouch  for  the  young  or  not,  is 
immaterial.  They  were  probably  marsupial  in  brain 
characters,  in  the  structure  of  their  reproductive  sys- 
tem, and  in  the  absence  of  placenta.  To  this  source 
the  existing  polyprotodont  marsupials  may  be  traced, 
through  such  forms  as  Myrmecobius.  The  multi- 
tuberculate  type  has  a  contemporary  history,  and  one 
distinct  from  that  of  the  Polyprotodontia,  and  its  an- 
cestry has  not  yet  been  discovered.  Their  earliest 
forms  (of  the  Jurassic  and  Triassic)  are  already  highly 
specialized.  They  probably  represent  the  Monotre- 
mata  of  their  time. 

Second.  The  immediate  didelphian  ancestors  of  the 
monodelphous  Mammalia  have  not  yet  been  certainly 
discovered.  In  the  oldest  of  the  latter  (of  the  Puerco 
epoch)  numerous  points  of  approach  to  the  insectivo- 
rous Jurassic  forms  occur,  especially  in  the  prevalent 
trituberculy  of  the  molars  in  both  epochs. 

Third.  The  phylogeny  of  the  clawed  group  has 
been  traced  back  to  a  common  ordinal  form  which  has 
been  called  the  Bunotheria.  Of  these  the  most  genera- 
lized are  the  Creodonta,  from  which  we  may  trace  the 
Carnivora,  the  Insectivora,  and  the  Tillodonta,  and 
probably  all  other  Unguiculata.  The  Ancylopoda  only 
have  undergone  the.  alternation  of  the  carpal  and  tar- 
sal  bones,  which  obtains  in  the  diplarthrous  Ungulata. 

Fourth.   The  phylogeny  of  the  hoofed  groups  car- 


PHYLOGENY.  141 

ries  us  back  to  the  order  Condylarthra,  the  hoofed 
cotemporary  of  the  Bunotheria.  The  even  and  odd 
toed  hoofed  mammals  are  traceable  back  to  the  Am- 
blypoda,  whose  oldest  representatives  are  the  Panto- 
donta  of  the  Puerco.  The  Proboscidia  and  Hyracoidea 
come  directly  from  the  Condylarthra.  Moreover,  the 
phalanges  of  the  lemurs  are  not  distinguishable  by  any 
important  characters  from  the  hoofs  of  the  Hyracoidea 
and  Condylarthra.  Not  only  this,  but  the  structure  of 
the  foot  in  these  three  groups  is  identical  in  regard  to 
the  mode  of  articulation  of  the  first  and  second  rows 
of  the  tarsal  and  carpal  bones^ 

Fifth.  The  characters  of  the  feet  of  the  Condylar- 
thra agree  with  those  of  unguiculate  placental  Mam 
malia,  and  bind  the  two  series  together.  The  synthesis 
of  the  ungulate  and  unguiculate  lines  is  accomplished 
by  exceptions  to  the  characters  which  define  them. 
Thus  the  hoofs  of  Pantolambda  (Amblypoda),  Peripty- 
chus  (Condylarthra),  and  Mesonyx  (Creodonta)  do  not 
differ  by  any  marked  character.  Claws  occur  in  the 
Hapalidae  of  the  quadrumanous  line,  and  the  ungues 
of  some  Glires  are  absolutely  intermediate  between 
the  hoofs  and  claws.  Many  Edentata  have  claws  on 
the  fore  feet  and  hoofs  on  the  hind  feet.  The  Condy- 
larthra with  tritubercular  molar  teeth  are  then  trace- 
able to  Bunotheria  with  tritubercular  teeth,  of  which 
many  are  known  from  the  Puerco  beds ;  and  the  quadri- 
tubercular  forms  from  corresponding  quadritubercular 
or  tritubercular  Bunotheria,  of  which  latter,  some  are 
known. 

Sixth.  The  anthropoid  line  may  be  traced  directly 
through  the  lemurs  to  the  Condylarthra.  The  changes 
which  have  taken  place  in  the  skeleton  are  slight,  and 


1 42    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

consist  among  other  points  in  a  rotation  of  the  second 
row  of  carpal  bones  inwards  on  the  first  row,  in  the 
anthropoid  apes  and  man,  similar  to  that  which  has 
occurred  among  the  Ungulata,  but  it  has  not  become 
so  pronounced. 

As  a  result  we  get  the  general  phylogenetic  scheme 
as  shown  on  the  following  page. 

In  this  diagram,  divisions  of  greater  and  lesser  rank 
are  mixed,  so  as  to  display  better  some  of  the  relation- 
ships. Thus  all  the  divisions  whose  names  stand  on 
the  right  side  of  the  middle  vertical  line  are  unguicu- 
lates  ;  and  those  on  the  left  side  of  the  line,  excepting 
Sirenia  and  Cetacea,  are  ungulates.  The  three  names 
in  the  middle  vertical  line  are  those  of  the  suborders 
of  the  Taxeopoda. 

A  review  of  the  characters  of  the  existing  Mam- 
malia as  compared  with  those  of  their  extinct  ances- 
tors displays  a  great  deal  of  improvement  in  many 
ways,  and  but  few  instances  of  retrogression.  The 
succession  in  time  of  the  Monotremata,  the  Marsupia- 
lia,  and  the  Monodelphia,  is  a  succession  of  advance 
in  all  the  characters  of  the  soft  parts  and  of  the  skele- 
ton which  define  them  (see  table  of  classification).  As 
to  the  monotremes  themselves,  it  is  more  than  prob- 
able that  the  order  has  degenerated  in  some  respects 
in  producing  the  existing  types.  The  history  of  the 
Monotremata  is  not  made  out,  but  the  earliest  forms 
of  which  we  know  the  skeleton,  Polymastodon  (Cope) 
of  the  Lower  Eocene,  is  as  specialized  as  the  most 
specialized  recent  forms.  The  dentition  of  the  Juras- 
sic forms,  Plagiaulax,  etc.,  is  quite  specialized  also, 
but  not  more  so  than  that  of  the  kangaroos.  The  pre- 
molars  are  more  specialized,  the  true  molars  less  spe- 
cialized than  in  those  animals.  The  history  of  Marsu- 


PHYLOGENY. 


M 

8 

0 

Z 

W 

U 

s 

I 

I 

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a 

i44    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

pialia  indicates  that  the  primitive  types  were  all  in- 
sectivorous, and  possessed  a  larger  number  of  molars 
than  any  of  the  recent  forms.  The  latter  have  then 
followed  the  same  course  as  the  placentals  in  the  re- 
duction of  the  number  of  teeth  and  specialization  of 
those  that  remain. 

Coming  to  the  Monodelphia,  the  increase  in  the 
size  and  complication  of  the  brain,  both  of  the  cere- 
bellum and  the  hemispheres,  is  a  remarkable  evidence 
of  advance.  But  one  retrogressive  line  in  this  respect 
is  known,  viz.,  that  of  the  order  Amblypoda,1  where 
the  brain  has  become  relatively  smaller  with  the  pas- 
sage of  time.  The  successive  changes  in  the  structure 
of  the  feet  are  all  in  one  direction,  viz. ,  in  the  reduc- 
tion of  the  number  of  the  toes,  the  elevation  of  the 
heel,  and  the  creation  of  tongue  and  groove  joints 
where  plain  surfaces  had  previously  existed.  The 
diminution  in  the  number  of  toes  might  be  regarded 
as  a  degeneracy,  but  the  loss  is  accompanied  by  a  pro- 
portional gain  in  the  size  of  the  toes  that  remain.  In 
every  respect  the  progressive  change  in  the  feet  is  an 
advance.  In  the  carpus  and  tarsus  we  have  a  gradual 
extension  of  the  second  row  of  bones  on  the  first,  to  the 
inner  side.  In  the  highest  and  latest  orders  this  pro- 
cess is  most  complete,  and,  as  it  results  in  a  more 
perfect  mechanical  arrangement,  the  change  is  clearly 
an  advance.  The  same  progressive  improvement  is 
seen  in  the  development  of  distinct  facets  in  the  cubito- 
carpal  articulation,  and  of  a  tongue  and  groove  ("troch- 
lear  crest ")  in  the  elbow-joint.  In  the  vertebra?  the 
development  of  the  interlocking  zygapophysial  articu- 
lations is  a  clear  advance. 

Progress  is  generally  noticeable  in  the  dental  struc- 

JSee  Naturalist,  Jan.,  1885,  p.  55. 


PHYLOGENY.  145 

tures ;  for,  the  earliest  dentitions  are  the  most  simple, 
and  the  later  the  more  complex.  Some  of  the  types 
retain  the  primitive  tritubercular  molars,  as  the  Cente- 
tidae,  shrews,  and  some  lemurs,  and  most  Carnivora 
(above),  but  the  quadritubercular  and  its  derivative 
forms  are  by  far  the  most  common  type  in  the  recent 
fauna.  The  forms  that  produced  the  complicated  mod- 
ifications in  the  Proboscidia  and  Diplarthra  appeared 
latest  in  time,  and  the  most  complex  genera,  Elephas, 
Bos,  and  Equus,  the  latest  of  all.  The  extreme  sec- 
torial  modifications  of  the  tritubercular  type,  as  seen 
in  the  Hyaenidae  and  the  Felidae,  are  the  latest  of  their 
line  also. 

Some  cases  of  degeneracy  are,  however,  apparent  in 
the  monodelphous  Mammalia.  The  loss  of  pelvis  and 
posterior  limbs  in  the  two  mutilate  orders  is  clearly  a 
degenerate  character,  since  there  can  be  no  doubt  that 
they  have  descended  from  forms  with  those  parts  of 
the  skeleton  present.  The  reduction  of  flexibility  seen 
in  the  limbs  of  the  Sirenia  and  the  loss  of  this  charac- 
ter in  the  fore  limbs  of  the  Cetacea  are  features  of  de- 
generacy for  the  same  reason.  The  teeth  in  both  or- 
ders have  undergone  degenerate  evolution  ;  in  the  later 
and  existing  forms  of  the  Cetacea  even  to  extinction. 

The  Edentata  have  undergone  degeneration.  This 
is  chiefly  apparent  in  the  teeth,  which  are  deprived  of 
enamel,  and  which  are  wanting  from  the  premaxillary 
bone.  A  suborder  of  the  Bunotheria,  the  Tillodonta 
of  the  Lower  Eocene  period,  display  a  great  reduc- 
tion of  enamel  on  the  molar  teeth,  so  that  in  much- 
worn  examples  it  appears  to  be  wanting.  Its  place  is 
taken  by  an  extensive  coat  of  cementum,  as  is  seen  in 
Edentata,  and  the  roots  of  the  teeth  are  often  undi- 
vided as  in  that  order. 


146    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

Local  or  sporadic  cases  of  degenerate  loss  of  parts 
are  seen  in  various  parts  of  the  mammalian  series,  such 
as  toothless  Mammalia  wherever  they  occur.  Such 
are  cases  where  the  teeth  become  extremely  simple, 
as  in  the  honey-eating  masupialTarsipes,  the  carnivore 
Proteles,  the  pteropod  bats,  and  the  aye-aye.  Also 
where  teeth  are  lost  from  the  series,  as  in  the  canine 
genus  Dysodus,  and  in  man.  The  loss  of  the  hallux 
and  pollex  without  corresponding  gain,  in  various  gen- 
era, may  be  regarded  in  the  same  light. 

In  conclusion,  the  progressive  may  be  compared 
with  the  retrogressive  evolution  of  the  Vertebrata,  as 
follows :  In  the  earlier  periods  and  with  the  lower 
forms,  retrogressive  evolution  predominated.  In  the 
higher  classes  progressive  evolution  has  predominated. 
When  we  consider  the  history  of  the  first  class  of  ver- 
tebrates, the  Tunicata,  in  this  respect,  and  compare 
it  with  that  of  the  last  class,  the  Mammalia,  the  con- 
trast is  very  great. 

h.    The  Phytogeny  of  the  Horse. 

As  an  example  of  special  phylogeny  I  select  that 
of  the  horse,  because  it  is  the  most  completely  repre- 
sented by  specimens  in  our  museums. 

I  have  already  pointed  out  that  the  alternate  type 
of  carpus  and  tarsus  of  the  Diplarthra  has  been  derived 
from  the  linear  of  the  Taxeopoda  by  a  displacement 
inwards  of  the  bones  of  their  second  rows.  In  the  pos- 
terior foot  this  has  changed  the  convex  surface  of  the 
head  of  the  astragalus  into  a  bifacetted  face.  Thus 
was  the  condylarthrous  astragalus  modified  into  that 
of  the  Diplarthra.  At  the  beginning  of  the  line  of 
the  horses  we  find  the  condylarthrous  genus  of  the 
Wasatch  Eocene,  Phenacodus  Cope,  to  differ  in  this 


PHYLOGENY.  147 

way  from  the  perissodactylous  genus  Hyracotherium 
Owen.  Phenacodontidae  are  indicated  as  the  ances- 
tors of  all  the  Ungulata  by  their  character  as  "buno- 
dont  pentadactyle  plantigrades,"  characters  in  which 
they  agree  with  the  ancestors  of  all  placental  mam- 
mals. That  they  are  not  the  ancestors  of  all  the  latter 
is  shown  by  the  fact  that  their  molar  type  is  quadritu- 
bercular;  but  one  has  to  go  backwards  but  a  short 
distance  in  time  to  the  Puerco  epoch,  to  find  their  tri- 
tubercular  ancestors.  Between  these  and  Phenaco- 
dus,  comes  the  quadritubercular  genus  Euprotogonia 
Cope,  of  the  Puerco,  which  has  simpler  premolar  teeth. 
Between  Phenacodus  and  Hyracotherium  there  is 
room  for  two  or  more  genera  with  fully  facetted  car- 
pals  and  tarsals,  longer  feet,  and  a  rudimental  first  toe 
on  the  anterior  foot,  and  first  and  fifth  toes  on  the  hind 
foot.  In  Hyracotherium  these  digits  have  disappeared. 
Further,  in  Hyracotherium  the  internal  cusps  of  the 
molars  are  more  or  less  connected  with  the  external 
by  low  and  indistinct  ridges,  which  in  the  superior 
molars  include  the  small  intermediate  tubercles  or 
conules.  Thus  is  the  lophodont  dentition  foreshad- 
owed. Hyracotherium  was  a  contemporary  of  Phe- 
nacodus and  continued  later  in  Eocene  time.  Some 
of  its  forms  developed  an  increased  complexity  of  the 
last  premolars  in  both  jaws,  forming  the  genus  Pliolo- 
phus,  and  foreshadowing  the  development  of  molar- 
like  premolars,  which  is  so  characteristic  of  the  later 
members  of  the  horse  line.  In  the  genus  Epihippus 
Marsh,  of  one  epoch  later  in  time  (the  Uinta),  two 
such  premolars  are  developed  in  each  jaw.  We  have 
seen  very  short  interspaces  next  the  canine  teeth  in 
Phenacodus,  and  these  have  become  longer  in  Hyra- 
cotherium and  Epihippus. 


148    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

With  the  opening  of  the  Neocene  age,  we  have  the 
descendant  of  Epihippus  in  Mesohippus  Marsh,  which 
differs  from  its  predecessor  as  follows.  There  are  but 
three  toes  on  all  the  feet ;  three  premolars  resemble 
the  true  molars  ;  the  crests  which  connect  the  internal 
pair  of  cusps  with  the  external  in  both  jaws,  are  much 
more  elevated,  and  soon  form  on  wearing  a  part  of  the 
pattern  of  the  crown.  Hyracotherium  already  walked 
on  the  ends  of  its  toes,  and  the  feet  of  Mesohippus 
continue  the  character.  The  crowns  of  all  the  molars 
are  short  like  those  of  its  ancestors.  In  the  Middle 
Neocene  formations  we  have  the  genus  Anchitherium 
Kaup,  where  the  incisor  teeth  show  the  addition  of  a 
ridge  or  cingulum  round  the  inner  side,  which  bounds 
a  cup  ;  forming  the  cupped  incisors  so  characteristic 
of  the  horses.  The  species  have  been  all  the  while 
growing  gradually  larger. 

Towards  the  end  of  Neocene  time  important  pro- 
gress was  made.  In  the  Loup  Fork  epoch  the  three 
toed  horses  were  very  numerous  in  species,  but  their 
lateral  toes  were  all  much  shortened  so  that  they  did 
not  reach  the  ground.  The  crests  of  the  molar  teeth 
were  much  stronger,  and  in  the  superior  series  the 
conules  had  assumed  a  greater  importance,  extending 
themselves  posteriorly  from  the  transverse  crests,  and 
showing  crescentic  sections,  resembling  those  of  the 
outer  cusps,  with  which  they  are  parallel.  The  an- 
terior conule  extended  so  far  posteriorly  as  to  join  the 
posterior  one,  resembling  in  this  respect  also  the  an- 
terior external  cusp.  So  the  crown  came  to  have  six 
modified  cusps  of  which  the  two  inner  are  the  smallest 
and  remain  unconnected  with  each  other.  The  crowns 
of  the  molars  vary  in  length  in  these  later  three-toed 
horses.  Some  are  short  like  the  Anchitheriums,  and 


PHYLOGENY.  149 

others  are  longer,  approaching  the  true  horses.  In  the 
valleys  between  these  high  cusps  cement  is  deposited, 
as  in  the  true  horses  and  other  mammals  with  long- 
crowned  molars.  There  are  two  types  of  these  later 
three-toed  horses.  In  one  the  posterior  inner  cusp  is 
not  joined  to  the  conule  by  a  transverse  crest  (genus 
Hippotherium  Kaup),  or  it  is  so  joined  (genus  Pro- 
thippus  Leidy). 

Plistocene  times  witnessed  the  perfection  of  the 
horse  line.  The  lateral  toes  dwindled  into  splints 
concealed  beneath  the  skin.  The  crowns  of  the  molar 
teeth  became  very  long,  and  in  the  upper  jaw  the  inner 
posterior  tubercle,  now  a  column,  joined  the  adjacent 
conule,  and  became  extended  very  much  in  fore  and 
aft  diameter.  The  small  anterior  premolar  disap- 
peared, and  the  canines  became  the  mark  of  the  male 
sex  only,  in  general.  The  lower  molars  acquire  some 
additional  complications,  and  the  feet  are  longer  than 
in  any  of  its  ancestors.  The  genus  Equus  L.  is  fin- 
ished, and  remains  a  permanent  member  of  the  human 
epoch,  from  which  its  only  relatives,  the  rhinoceros 
and  the  tapir,  are  gradually  disappearing. 

This  history  may  be  duplicated  in  manner  and 
mode,  by  the  lines  of  the  camels,  the  dogs  and  bears, 
the  cats,  the  beaver,  etc. 

Examination  of  all  these  genealogical  lines  reveals 
a  certain  definiteness  of  end  and  directness  of  approach. 
We  discover  no  accessions  of  characters  which  are 
afterwards  lost,  as  would  naturally  occur  as  a  result  of 
undirected  variation.  Nor  do  we  discover  anything 
like  the  appearance  of  sports  along  the  line,  the  word 
sport  being  used  in  the  sense  of  a  variation  widely  di- 
vergent from  its  immediate  ancestor.  On  the  con- 
trary, the  more  thorough  becomes  our  knowledge  of 


150    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

the  series,  the  more  evident  does  it  become  that  pro- 
gressive evolution  has  advanced  by  minute  increments 
along  a  definite  line,  and  that  variations  off  this  line 
have  not  exerted  an  appreciable  influence  on  the  re- 
sult. 

/.    The  Phytogeny  of  Man. 

In  man  the  feet  retain  the  pentadactyle  plantigrade 
type  with  scarcely  grooved  astragalo-tibial  articula- 
tion, which  characterizes  the  Mammalia  of  the  Puerco 
epoch,  and  most  of  those  of  the  Lower  Eocene.1  His 
dentition  is  not  lophodont,  but  is  simply  bunodont,  like 
that  of  the  Phenacodontidae  of  the  Lower  Eocene.  It 
is  only  in  the  structure  of  the  brain  and  the  reproduc- 
tive system  that  man  shows  an  advance  over  the  Eocene 
type.  In  the  former  he  greatly  excels  any  mammal 
that  has  appeared  since ;  a  superiority  already  apparent 
in  one  of  his  early  ancestors,  the  anaptamorphous  lemur 
of  the  Lower  Eocene.  In  the  reproductive  system  he 
is  about  on  a  par  with  the  higher  Artiodactyla,  although 
the  male,  in  the  persistent  union  of  the  genital  and  urin- 
ary efferent  ducts  is  not  so  much  specialized  as  some  of 
the  latter,  where  they  are  distinct.  It  is  an  interesting 
fact  that  man  displays  in  his  dentition  strong  tenden- 
cies to  a  greater  specialization  by  simplification  beyond 
the  ordinary  quadrumanous  type,  by  reduction  in  the 
number  of  the  true  molars  and  incisors.  Thus  the  M.-Ms 
not  unfrequently  absent  in  the  highest  races,  and  some 
families  display  a  rudimental  condition  and  absence  of 
the  I.i. 

Much  importance  attaches  to  the  composition  of 
the  molar  dentition.  Many  years  ago,  Owen2  called 

IThis  fact  was  first  pointed  out  by  myself  in  the  Penn  Monthly  Magazine, 
1875  ;  see  Origin  of  the  Fittest,  p.  268. 
lOdontography,  1840-5,  p.  454. 


PHYLOGENY.  151 

attention  to  the  fact  that  in  the  dark  races  the  roots  of 
the  last  superior  molar  are  distinct  from  each  other, 
while  in  the  Indo-Europeans  they  are  known  to  be 


Fig.  38.— Fig  a,  skull  of  Anaptomorphus  homunculus  Cope,  natural  size. 
Fig.  />,  same,  oblique  view,  displaying  the  large  cerebral  hemispheres.  Fig.  c, 
superior  view  of  skull,  natural  size.  Fig.  d,  inferior  view,  three-halves  natural 
size.  Lower  figs,  a,  b,  and  c,  left  branch  of  lower  jaw  of  Anaptomorphus  eemu- 
lus  Cope,  twice  natural  size;  a,  from  left  side;  b,  inner  side;  c,  from  above. 

more  or  less  fused  together.  These  now  well-known 
characteristics  of  human  dentition  constitute  one  of 
the  examples  of  transition  from  a  simian  to  a  human 


1 52    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

type.  I  have  pointed  out  a  corresponding  modifica- 
tion in  the  structure  of  the  crown  of  the  superior  true 
molars,  viz. :  the  transition  from  a  quadritubercular  to  a 
tritubercular  structure  in  passing  from  the  lower  to  the 
higher  races.  As  this  point  has  some  interesting  im- 
plications in  the  earlier  phylogeny  of  man,  and  as  its 
value  has  been  disputed,  I  give  it  a  little  attention. 

The  facts  of  the  case  are  as  follows  :  I  have  dem- 
onstrated1 the  fact  that  all  forms  of  dentition  exhibited 
by  the  eutherian  mammals  have  been  derived  from  a 
primitive  tritubercular  type.  Professor  Osborn  says 
that  he  expects  to  be  able  to  do  the  same  for  the  multi- 
tuberculate  (?  Prototherian)  dentition.  I  have  also 
shown  that  man  exhibits  a  tendency  to  revert  from  his 
primitive  quadritubercular  molar  to  this  tritubercular 
type.2  As  to  the  significance  of  these  facts,  I  have 
expressed  the  view  that  this  acquisition  of  a  tritubercu- 
lar molar  is  a  reversion  to  the  lemurine  type.  This 
conclusion  is  necessary  because  the  lemurs  are  the  last 
of  the  families  in  the  line  of  the  ancestry  of  man  which 
present  this  dentition.  The  monkeys  and  anthropoid 
apes  are  all  quadritubercular,  except  a  few  limited  col- 
lateral branches  of  the  former,  which  still  retain  the 
lemurine  type.  There  are  also  a  few  collateral  types 
of  lemurs  which  have  acquired  one  or  more  quadri- 
tubercular molars,  but  they  are  not  typical.  In  many 
tritubercular  mammals,  a  precocious  form  or  two  can 
be  found,  which  has  acquired  the  fourth  tubercle.  But 
the  further  back  we  go  in  time,  the  fewer  they  become, 
until,  in  the  Puerco  fauna,  of  eighty-two  species  of 

I  Proceeds.  Amer.  Philos.  Soc.,  Dec.,  1883  ;  Origin  of  the  Fittest >  1887,  pp 
245.  347,  359- 

"^American  Journal  of  Morphology,  II.,  i8B3,  p.  7. 


PHYLOGENY.  153 

eutherian  mammals,  but  four  have  true  quadritubercu- 
lar  superior  molars. 

I  take  this  opportunity  of  saying,  however,  that  re- 
version is  not  necessarily  a  result  of  heredity.  It  may 
be  simply  a  retrogression  on  a  line  of  advance  already 
laid  down.  What  influence  lemurine  heredity  may 
have  had  in  the  case  of  man,  it  is  not  easy  to  know. 
But  it  must  be  borne  in  mind  that  various  forms  of 
degeneracy  of  molar  teeth  are  possible  other  than  the 
resumption  of  the  tritubercular  type,  yet  the  normal 
reduction  generally  presented  is  just  this  lemurine  and 
primitive  eutherian  condition.  The  simplicity  of  the 
elements  involved,  has  something,  but  not  everything, 
to  do  with  this  reversion. 

Dr.  Paul  Topinard  has  made  an  investigation  l  of 
the  characters  of  the  crowns  of  the  molars  in  man,  and 
has  reached  general  conclusions  identical  with  my  own. 
He  remarks  (p.  665):  "It  is  demonstrated,  in  conclu- 
sion, that  the  teeth  of  man  are,  at  present,  in  process 
of  transformation,  and  that  in  some  future  which  is  re- 
mote the  inferior  molars  shall  certainly  be  quadri- 
cuspid,  and  the  superior  molars  tricuspid.  It  will  be 
curious  to  have  the  statistics  as  to  prehistoric  man; 
unfortunately,  their  crania  are  rare,  and  their  molars 
generally  much  worn."  In  the  details  of  his  examina- 
tion, there  are  some  divergencies  from  my  results. 
Thus  he  finds  the  quadritubercular  second  and  third 
superior  molar  relatively  of  more  frequent  occurrence 
in  Europeans  than  I  did.  But  the  absence  of  Europeo- 
Americans  from  his  tables  reduces  the  percentage  of 
trituberculars  in  the  Indo-Europeans.  He  makes  no 
report  of  Esquimaux.  Had  he  observed  this  type,  he 
would  have  found  a  higher  per  cent,  of  tritubercular 

ZL'Anthropologze,  1892,  p.  641  (Nov.,  Dec.). 


i54    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

upper  molars  than  in  any  race  that  he  has  recorded. 
He  confirms  my  conclusion  as  to  the  high  percentage 
of  quadritubercular  superior  molars  in  the  Malays, 
Polynesians,  and  Melanesians. 

The  relation  of  this  fact  to  phylogeny  is  to  confirm 
Haeckel's  hypothesis  of  the  lemurine  ancestry  of  man. 
I  have  advanced  the  further  hypothesis  that  the  An- 
thropomorpha  (which  include  man  and  the  anthropoid 
apes)  have  been  derived  directly  from  the  lemurs,  with- 
out passing  through  the  monkeys  proper.  This  close 
association  of  man  with  the  apes,  is  based  on  various 
considerations.  One  of  them  is  that  the  skeleton  of 
the  anthropoid  apes  more  nearly  resembles  that  of 
man  in  the  most  important  respects  than  it  does  that 
of  the  monkeys.  This  is  especially  true  of  the  verte- 
bral column,  where  the  anapophyses  are  wanting  in 
the  Anthropomorpha  (insignificant  rudiments  remain- 
ing on  one  or  two  vertebrae,  as  pointed  out  by  Mivart), 
while  they  are  well  developed  in  the  monkeys  and 
lemurs.  The  molar  teeth  of  the  apes  and  man  resem- 
ble each  other  more  than  either  do  those  of  the  mon- 
keys, since  they  lack  the  crests  which  connect  the 
cusps,  which  are  general  in  the  latter. 

The  frequent  presence  of  the  tritubercular  molar  in 
man  suggests  the  superior  claim  of  the  lemurs  over  the 
monkeys  to  the  position  of  ancestor.  Another  signifi- 
cant fact  pointing  in  the  same  direction  is  the  existence 
of  large-brained  lemurs  with  a  very  anthropoid  denti- 
tion (Anaptomorphidae)  in  our  Eocene  beds,  which  have 
the  dental  formula  of  man  and  the  Old  World  monkeys 
and  apes.  This  resemblance  is  very  remarkable,  much 
exceeding  that  lately  observed  by  Ameghino  in  certain 
extinct  forms  of  monkeys  in  Patagonia,  which  appear 
to  be  ancestors  of  the  existing  South  American  mon- 


PHYLOGENY.  155 

keys  (Cebidae),  and  possibly  of  the  Old  World  monkeys 
also.  The  superior  molars  of  the  Anaptomorphus  are 
tritubercular,  while  the  premolars,  canines,  and  in- 
cisors are  essentially  anthropomorphous,  and  rather 
human  than  simian.  Anaptomorphus  is  probably  at 
the  same  time  the  ancestor  of  the  Malaysian  lemurine 
genus  Tarsius,  and  M.  Topinard  remarks  that  Tarsius 
has  as  good  claims  to  be  regarded  as  ancestral  to 
Homo  as  Anaptomorphus.  But  M.  Topinard  must  be 
aware  that  in  the  existing  genus  the  character  of  the 
canine  and  incisive  dentition  is  very  unlike  that  of  the 
Anaptomorphus  and  Homo.  It  is  specialized  in  a 
different  direction.  The  dentition  of  Anaptomorphus 
being  so  generalized  as  compared  with  Tarsius,  I  sus- 
pect that  its  skeleton  will  be  found  to  present  corre- 
sponding characters.  Of  course,  if  it  be  found  here- 
after to  have  the  foot  structure  of  Tarsius  (which  I  do 
not  anticipate),  it  cannot  be  included  in  the  ancestry 
of  the  Anthropomorpha. 

It  must  be  further  observed  that  the  ancestral  line 
of  the  Anthropomorpha  cannot  be  traced  through  any 
existing  type  of  Lemuridae,  but  through  the  extinct 
forms  of  the  Eocene  period.1  This  is  on  account  of 
the  peculiar  specialization  of  the  inferior  canines,  which 
are  incisor-like,  and  because  of  the  peculiar  character 
of  the  incisors  themselves,  in  the  modern  lemurs  in 
the  restricted  sense.  But  we  have  numerous  lemurine 
types  of  the  Eocene  of  both  America  and  Europe 
which  satisfy  the  conditions  exactly,  so  far  as  the  den- 
tition is  concerned.  These  are  mostly  referable  to  the 
family  Adapidae. 

Unfortunately,  we  do  not  know  the  entire  skeletons 

1  On  the  Primitive  Types  of  the  Orders  of  the  Mammalia  Educabilia,  1873, 
p.  8. 


156    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

of  these  Eocene  lemurs,  but  as  far  as  we  have  them 
(genera  Tomitherium  and  Adapis)  they  are  monkey- 
like.  But  we  have  what  is  almost  as  useful,  the  skel- 
eton of  their  Eocene  and  Puerco  ancestors,  the  Con- 
dylarthra.  I  long  since  pointed  out  that  the  latter 
order  (not  the  genus  Phenacodus,  as  Lydekker  has 


ae  pe 

Fig- 39- — Tomitherium  rostratum  Cope,  one  of  the  Adapidae,  mandible, 
natural  size;  a,  from  left  side;  b,  from  above.  Original,  from  Report  U.  S. 
Geol.  Survey  Terrs.,  Vol.  III. 

represented  me  as  saying)  must  be  the  ancestors  of 
the  lemurs,  basing  my  views  expressly  on  the  general 
structure  of  the  Phenacodus,  Periptychus,  and  Menis- 
cotherium.  The  structure  of  the  ungual  phalanges  of 
Periptychus  is  very  significant,  and  even  more  so  is 
that  in  Meniscotherium,  as  recently  shown  by  Marsh, 


PHYLOGENY. 


157 


who  adopts  (without  credit)  my  hypothesis  of  lemurine 
affinities  of  the  Condylarthra  (which  he  renames  the 
Mesodactyla).  From  Condylarthra  back  to  Creodonta 
is  an  easy  transition,  and  I  have  always  assumed  that 
the  Creodonta  were  derived  from  generalized  polypro- 
todont  Mursupialia.  This  view 
has  been  entirely  confirmed  by 
the  recent  discoveries  of  Ame- 
ghino  in  Patagonia,  where  he 
has  found  forms  whose  remains 
may  be  referred  with  equal  pro- 
priety to  the  one  group  or  the 
other.  M.  Topinard  has  been 
rather  hasty  in  reaching  the 
marsupial  ancestry  in  suppos- 
ing that  Phenacodus  belongs  to 
that  order.  All  the  evidence 
shows  that  Phenacodus  is  a 
generalized  ungulate  placental. 
To  return  to  the  more  im- 
1  Jl^  mediate  ancestry  of  man.  I 

^J    fflV     m  have  expressed,1  and  now  main- 

tain as  a  working  hypothesis, 
Jl  MV        *^at   all   the   Anthropomorpha 

AH  b^B         were  descended  from  the  Eo 

w^j^  Cj0 

cene  lemuroids.  In  my  sys- 
tem2 the  Anthropomorpha  in- 
cludes the  two  families  Homi- 
nidae  and  Simiidae.  The  sole 
difference  between  these  families  is  seen  in  the  struc- 
ture of  the  posterior  foot;  the  Simiidae  having  the 

1  American  Naturalist,  1885,  p.  467. 

2  Origin  of  the  Fittest,  1887,  p.  346,  from  American  Naturalist,  1885,  p.  34^, 
where  the  classification  of  the  Taxeopoda  should  be  in  a  foot-note;  loc.  cit., 
1880,  October. 


Fig.  40. — Tomitherium  ros- 
tratum  Cope,  fore  arm,  five- 
sixths  natural  size.  Original, 
b,  ulna;  c,  radius. 


158    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION 


hallux  opposable,  while 
in  the  Hominidse  the 
hallux  is  not  opposable. 
This  is  not  a  strong 
character,  since  it  de- 
pends on  a  slight  differ- 
ence in  the  form  of  the 
entocuneiform  bone.  In 
some  vertebrates,  as  the 
tree-frogs,  the  same  and 
similar  characters  (ge- 
nus Phyllomedusa)  are 
not  regarded  as  of  fam- 
ily value.  It  is  then 
highly  probable  that 
Homo  is  descended 
from  some  form  of  the 
Anthropomorpha  now 
extinct,  and  probably 
unknown  at  present,  al- 
though we  do  not  yet 
know  all  the  charac- 
ters of  some  extinct 
supposed  Simiidae,  of 
which  fragments  only 
remain  to  us.  It  cannot 
now  be  determined 
whether  man  and  the 
Simiidae  were  both  de- 
scended from  a  genus 
with  opposable  hallux, 
or  without  opposable 

,  Or  Whether  from 


um  rostratum  Cope, 
five-sixths  natural  size;  a,  ilium;  b,  femur 

a  genus  presenting  an    original. 


PHYLOGENY.  159 

intermediate  character  in  this  respect.  This  genus 
was,  in  any  case,  distinct  from  either  of  the  two  existing 
genera  of  Simiidae,  Simia  and  Hylobates,  since  these 
present  varied  combinations  of  anthropoid  resem- 
blances and  differences,  of  generic  and  specific  value. 
Professor  Virchow  in  a  late  address1  has  thrown 
down  the  gage  to  the  evolutionary  anthropologists  by 
asserting  that  "scientific  anthropology  begins  with 
living  races,"  adding  "that  the  first  step  in  the  con- 
struction of  the  doctrine  of  transformism  will  be  the 
explanation  of  the  way  the  human  races  have  been 
formed,"  etc.  But  the  only  way  of  solving  the  latter 
problem  will  be  by  the  discovery  of  the  ancestral 
races,  which  are  extinct.  The  ad  captandum  remarks 
of  the  learned  professor  as  to  deriving  an  Aryan  from 
a  Negro,  etc.,  remind  one  of  the  criticisms  directed 
at  the  doctrine  of  evolution  when  it  was  first  presented 
to  the  public,  as  to  a  horse  never  producing  a  cow, 
etc.  It  is  well  known  to  Professor  Virchow  that  hu- 
man races  present  greater  or  less  approximations  to 
the  simian  type  in  various  respects.  Such  are  the 
flat  coossified  nasal  bones  of  the  Bushmen  ;  the  qua- 
dritubercular  molars  of  the  Polynesians ;  the  flat  ilia 
and  prognathous  jaws  of  the "  Negro ;  the  flat  shin- 
bones  of  various  races ;  the  divergent  hallux  of  some 
aborigines  of  farther  India,  etc.  Professor  Virchow 
states  that  the  Neanderthal  man  is  a  diseased  subject, 
but  the  disease  has  evidently  not  destroyed  his  race 
characters;  and  in  his  address  he  ignores  the  important 
and  well-authenticated  discovery  of  the  man  and  wo- 
man of  Spy.  These  observations  are  reinforced  by 
recent  discovery  of  a  similar  man  by  DuBois  at  Trinil 

I  Popular  Science  Monthly,  January,  1893,  p.  373,  translated. 


160    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

in  the  island  of  Java.     To  these  ancient  people  I  will 
now  devote  some  space. 

What  had  been  long  suspected  is  now  established, 


Fig.  42. — Megaladapis  madagascariensis  Forsyth  Major,  yz  natural  size;   lemuroid  from  Plis 
tocene  bed  of  Madagascar,  with  tritubercular  superior  molars.     From  Forsyth  Major. 

through  the  discovery  and  descriptions  of  Messrs. 
Fraipont  and  Lohest  of  Liege  ;  viz.  that  there  dwelt  in 
Europe  during  Paleolithic  times  a  race  of  men  which 


PHYLOGENY.  161 

possessed  a  greater  number  of  simioid  characteristics 
than  any  which  has  been  discovered  elsewhere.  The 
important  discovery  in  the  grotto  of  Spy  of  two  skele- 
tons, almost  complete,  served  to  unify  knowledge  of 
this  race,  which  had  previously  rested  on  isolated  frag- 
ments only.  These  skeletons  proved  what  had  been 
previously  only  surmised,  that  the  lower  jaws  of  Nau- 
lette,  and  of  Shipka,  and  probably  the  skeleton  of 
Neanderthal,  belong  to  one  and  the  same  race.  The 


Fig.  43.— Skull  of  the  man  of  Spy.     From  Prof.  G.  F.  Wright's  Man  and 
the  Glacial  Period.     From  a  photograph. 

simian  characters  of  these  parts  of  the  skeleton  are 
well  known.  These  are  the  enormous  superciliary 
ridges  and  glabella  ;  the  retreating  frontal  region ;  the 
thickness  of  the  cranial  wall ;  the  massive  mandibular 
ramus  with  rudimentary  chin,  and  the  large  size  of  the 
posterior  molars.  Messrs.  Fraipont  and  Lohest  have 
added  other  characters  to  these,  viz. :  the  tibia  shorter 
than  in  any  other  known  human  race ;  the  sigmoid 
flexure  of  the  femur ;  the  divergent  curvature  of  the 
bones  of  the  fore-arm,  and  most  important,  a  very 


162    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

peculiar  form  of  the  posterior  face  of  the   mandibular 
symphysis,  already  pointed  out  by  Topinard  in  the  jaw 


of  Naulette.      On  these  characters   the  following  re- 
marks may  be  made.1 

I.   The  prominent   superciliary  crests,    which   are 

1  Archives  Beiges  de  Biologie,  VII.,  1886,  p.  731,  Gand. 


PHYLOGENY.  163 

characteristic  of  the  Neanderthal  race.  No  existing 
race  presents  such  a  development,  neither  the  Papu- 
ans, Australians,  nor  Negroes  of  any  race.  But  we 
find  the  superciliary  crests  and  underlying  sinuses 
identical  in  adult  female  orangs  and  chimpanzees  and 
young  male  gorillas.  In  the  female  chimpanzees  the 
crests  are  almost  inferior  in  size  to  those  of  the  man  of 
Spy. 

II.  The  retreating  forehead  of  the  two  crania  of 
Spy  is  not  found  in  any  existing  human  race,  while  it 
is  typical  of  that  of  Neanderthal.      It  is  characteristic 
of  female  orangs  and  gorillas  and  of  the  young  males 
of  both  species,  and  of  adult  males  and  female  chim- 
panzees.     It  appears  in  existing  men  in  rare  and  iso- 
lated cases;    [probably  as  survivals]. 

III.  The  prominent  transverse  superior  semicircu- 
lar crest  of  the  occipital  bone  is  found  in  existing  races 
among  the  Fellahs  of  Africa  and  the  Nigritos.      It  is 
characteristic  of  the  Neanderthal  skulls,  and  presents 
exactly  the   same   characters  as  the  young   male  and 
female  orang  and  gorilla  and  young  male  and  adult 
female  of  the  chimpanzee. 

IV.  No  human  race  presents  the  characters  of  the 
lower  jaw  exhibited  by  those  of  Spy,  Naulette,  and 
Shipka.      In  this  part  of  their  osteology  the  anthro- 
poids depart  widely  from  man,  the  most  conspicuous 
point  in  the  latter  being  the  presence  of  a  chin.      Ac- 
cordingly, the  angle  formed  by  the  anterior  face  of  the 
symphysis  with  the  inferior  border  of  the  horizontal 
ramus,  is   less  than   a  right  angle  in  man,  and  much 
more  than  a  right  angle  in  the  anthropoids.   According 
to  Topinard,  this  angle  in  fifteen  Parisians  is  71.4°;  in 
fifteen  African  Negroes,  82.2°;   in  fifteen   Neocaledo- 
nians,  83.9°;  in  the  jaw  of  Naulette,  94°.     In  the  best 


164    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

preserved  jaw  of  Spy  the  angle  is  107°,  if  measured 
from  the  inferior  symphysial  border,  or  90°  if  meas- 


C 


n 


M 


Fig.  45. — Vertical  sections  of  symphysis  mandibuli  of  gorilla  (Fig.  A),  and 
orang  (Fig.  B],  of  chimpanzee  (Fig.  C),  of  Spy  man  No.  i  (Fig.  D),  and  Spy  man 
No.  2  (Fig.  E).  From  Fraipont  and  Lohest. 

ured  from  the  inferior  border  of  the  ramus.  There 
is  no  chin  in  the  jaw  of  the  Spy  race,  and  the  large 
angle  approaches  without  nearly  equaling  that  of  the 


PHYLOGENY.  165 

anthropoids.  But  the  posterior  face  of  the  symphysis 
presents  the  most  remarkable  peculiarity.  In  the 
symphysis  of  the  apes  (Fig.  54,  A,  B,  C}  the  posterior 
border  is  a  continuous  slope  from  the  alveolar  border 
to  the  inferior  margin,  interrupted  by  a  slight  concav- 
ity below  the  middle.  In  the  human  jaw  this  line 
slopes  backward  to  near  the  middle,  where  are  situated 
the  small  tuberosities  for  the  insertion  of  the  genio- 
glossal  muscles.  (B  in  the  accompanying  figures.)  The 
surface  then  slopes  rapidly  forward  to  pass  into  the 
narrow  inferior  border  of  the  chin  (Fig.  46,  Pt  G).  In 
the  jaws  Naulette  and  Spy  the  structure  is  exactly  in- 
termediate between  the  two,  and  quite  different  from 
both  (Fig.  45,  D,  £).  It  commences  above  with  a  pos- 
terior slope  similar  to  that  of  the  apes,  exhibiting 
what  is  called  by  Topinard  "  internal  prognathism," 
as  it  appears  in  the  lower  human  races.  The  surface 
then  descends  abruptly,  forming  a  vertical  concavity, 
which  is  bounded  a  considerable  distance  below  by 
another  protuberance,  the  insertion  of  the  genioglossal 
muscles.  This  concavity  is  not  present  in  the  human 
symphysis,  while  it  is  less  developed  in  the  simian. 
The  surface  then  slopes  forward,  as  in  the  human  sym- 
physis, but  this  portion  is  shorter  than  in  human  jaws 
generally.  It  is  represented  by  a  convex  face  in  the 
simian  jaw.  This  character,  taken  in  connection  with 
the  others  cited,  goes  a  long  way  toward  justifying  the 
separation  of  the  Neanderthal  race  as  a  distant  species, 
as  has  been  done  by  some  author  under  the  name  of 
Homo  neanderthalensis.  This  name  is  objectionable  but 
must  be  retained. 

To  these  observations  Messrs.  Fraipont  and  Lohest 
add  the  following. 

V.   The   curvature   of   the  ulna  and  radius,  which 


T  66    PR  IMA  RY  FAC  TORS  OF  OR G A  NIC  E  VOL  UTION. 


produces  a  wide  interosseous  space,  is  not  found  in  any 
human  race,  but  is  common  to  the  apes.  On  the  con- 
trary, the  shortness  of  these  bones  is  entirely  human. 

VI.  The  anterior  convexity  of  the  femur,  with  its 
round  section,  is  only  found  among  living  races  among 
the  Nigritos  of  the  Philippine  Islands.     It  is  seen  in  a 
less  degree  in  femora  of  Neolithic  men,  and  occasional 
instances  are  seen  among  existing  Europeans.     It  is 
the  normal  condition  in  the  apes. 

VII.  The  tibia  is  shorter  in  its  relation  to  the  femur 
than   in   any  human  race,  and  is  more  robust  than  in 


M 


Fig.  46. — Sections  of  symphysis  mandibuli  of  modern  Liegois  (Fig.  F) 
and  of  an  ancient  Parisian  (Fig.  G).    From  Fraipont  and  Lohest.    . 

most  of  them.  This  character,  with  the  oval  section, 
while  not  identical  with  what  is  seen  in  the  apes,  forms 
an  approximation  to  it. 

Messrs.  Fraipont  and  Lohest  have  pointed  out  the 
general  characters  of  the  dentition  of  the  man  of  Spy. 
They  show  that  the  molars  increase  in  size  posteriorly 
to  the  same  extent  that  they  do  in  the  apes,  which  is 
the  reverse  of  what  is  usual  in  man,  where  they  dimin- 
ish posteriorly,  or,  in  a  few  lower  races  (Australians, 
etc.),  remain  equal.  They  show  that  the  superior  mo- 
lars are  all  quadritubercular,  and  that  the  internal  root 


168    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

is  distinct  in  all  of  them.  Through  the  kindness  of 
M.  Lohest  I  received  casts  and  photographs  of  these 
teeth,  and  I  give  here  figures  of  the  former  (Fig.  47), 
which  are  more  satisfactory  than  those  in  the  memoir 
from  which  I  have  already  quoted  so  fully,  where,  in- 
deed, the  grinding  faces  are  not  represented  at  all. 

The  figures  accompanying1  show  the  large  size  of 
the  last  superior  molar,  which  exceeds  in  its  propor- 
tions those  of  the  corresponding  tooth  in  the  chimpan- 
zee. The  fourth  tubercle,  or  hypocone,  is  especially 
large.  In  the  male  the  crowns  are  more  produced 
posteriorly  than  in  man  generally,  and  remind  one  of 
the  character  seen  in  the  orang.  The  strong  divergence 
of  the  internal  root  of  the  last  molar  is  shown  in  No. 
2  a,  and  the  corresponding  character  in  a  Maori  and  a 
Fan  from  tropical  Africa  is  shown  in  Nos.  3  and  5  a. 
The  quadritubercular  crown  of  the  last  superior  molar 
of  a  Tahitian  is  shown  in  No.  4  a  ;  and  the  roots,  which 
are  exceptionally  fused  nearly  as  much  as  in  the  typi- 
cal Indo-European,  are  shown  in  No.  4. 

Dr.  Eugene  Dubois  of  the  Army  of  the  Netherlands 
has  recently  published  in  Batavia,  Java,  in  a  brochure 
in  quarto,  an  account  of  some  bones  of  an  interesting 
quadrumanous  mammal  allied  to  man,  which  were 
found  in  a  sedimentary  bed  of  material  of  volcanic  ori- 
gin of  probably  Plistocene  age,  near  a  village  called 
Trinil.  The  remains  consist  of  a  calvarium  which  in- 
cludes the  supraorbital  ridges  and  a  part  of  the  occi- 
put ;  a  last  superior  upper  molar,  and  a  femur.  The 
tooth  was  found  close  to  the  skull  and  belongs  probably 
to  the  same  individual  as  the  latter,  while  the  reference 
of  the  femur  is  more  uncertain,  as  it  was  found  some 
fifty  feet  distant. 

IFrom  The  American  Naturalist,  April,  1893. 


PHYLOGENY,  169 

The  characters  of  the  skull  are  closely  similar  to 
those  of  the  men  of  Neanderthal  and  of  Spy,  but  the 
walls  are  not  so  thick  as  those  of  the  former,  and  more 
nearly  resemble  those  of  the  latter.  The  frontal  region 
is,  therefore,  much  depressed,  and  it  is  also  much  con- 
stricted posterior  to  the  postorbital  borders.  The  su- 
tures are  obliterated.  Dr.  Dubois  states  that  the  cranial 
capacity  is  just  double  that  of  the  gorilla,  and  two-thirds 
that  of  the  lowest  normal  of  man,  bridging  the  gap 
which  has  long  separated  the  latter  from  the  apes. 
Thus  the  capacity  of  the  former  is  500  cubic  centime- 
tres, and  the  latter  is  1500  cubic  centimetres.  In  the 
Java  man  the  capacity  is  1000  cubic  centimetres.  The 
last  upper  molar  has  widely  divergent  roots,  as  in  apes 
and  inferior  races  of  man,  and  the  crown  is  large,  with 
the  cusps  not  clearly  differentiated,  showing  a  character 
commonly  observed  in  the  lower  molars  of  the  gorilla. 
The  femur  is.  long,  straight,  and  entirely  human.  This 
discovery  of  Dr.  Dubois  adds  to  our  knowledge  of  the 
physical  characters  of  the  Paleolithic  man,  and  espe- 
cially to  his  geographical  range. 

As  regards  the  proper  appellation  of  this  being, 
Dr.  Dubois  is  not  happy.  He  proposes  for  him  a 
new  genus  Pithecanthropus  (after  Haeckel),  and  even 
a  new  family,  Pithecanthropidae,  without  having  shown 
that  he  is  not  a  member  of  the  genus  Homo.  It  is 
not  certain  that  he  is  not  an  individual  of  the  species 
Homo  ncanderthalensis.  His  cranial  capacity  is  less,  it 
is  true,  than  that  of  the  man  of  Spy,  but  Virchow  has 
pointed  out  that  some  of  the  Nigritos  possess  a  remark- 
ably small  cranial  capacity,  as  little  as  950  cubic  centi- 
metres, and  an  inhabitant  of  New  Britain  only  860 
cubic  centimetres,  a  capacity  even  smaller  than  that  of 
the  man  of  Trinil.  Until  we  learn  the  characters  of 


170    PR f MARY  FACTORS  OF  ORGANIC  EVOLUTION. 

the  lower  jaw  of  the  latter  we  shall  be  in  doubt  as  to 
whether  this  individual  pertains  to  the  Homo  sapiens 
or  the  Homo  neanderthalensis. 

The  characters  of  the  dentition,  cranium,  and  limbs 
which  have  been  observed  in  the  Paleolithic  man,  are 
not  without  parallel  in  existing  races,  though  the  char- 
acters do  not  generally  occur  together  in  the  latter. 
The  supposition  that  all  the  Paleolithic  men  so  far 
found  are  all  pathological  subjects  is  not  a  probable 
solution  of  the  question,  although  this  type  was  no 
doubt  subject  to  pathological  conditions  such  as  have 
been  found  in  the  leg-bones  of  the  men  of  Neanderthal 
and  Trinil.  The  characters  of  the  symphysis  of  the 
lower  jaw  are  quite  sufficient  to  separate  the  Neander- 
thal man  as  a  distinct  species  of  the  genus  Homo.1 
This  character  is  not  pathological  but  it  is  zoological, 
and  places  that  species  between  Homo  sapiens  and  the 
apes. 

In  conclusion,  it  may  be  observed  that  we  have  in 
the  Homo  neanderthalensis  a  greater  number  of  simian 
characteristics  than  exist  in  any  of  the  known  races  of 
the  Homo  sapiens,  although,  so  far  as  known,  he  be- 
longs to  the  genus  Homo.  The  posterior  foot,  so  far 
as  preserved,  indicates  this  to  be  the  case.  The  foot- 
character,  which  distinguishes  the  genera  Homo  and 
Simia  still  remains.  There  is  still,  to  use  the  language 
of  Fraipont  and  Lohest,  "  an  abyss  "  between  the  man 
of  Spy  and  the  highest  ape  ;  though,  from  a  zoological 
point  of  view,  it  is  not  a  wide  one. 

The  flints  which  were  discovered  in  the  stratum  of 
cave  deposit  containing  the  human  remains,  are  of  the 
Paleolithic  type  known  as  Mousterien  in  France,  which 

IThis  view  was  first  insisted  on  in  an  article  on  the  Genealogy  of  Man  in 
the  American  Naturalist,  1893,  p.  331. 


PHYLOGENY. 


171 


are  of  later  origin  than  the  Chelle"en  or  older  Paleo- 
lithic. The  older  Paleolithic  man  is  not  yet  known. 
It  is  interesting  to  observe  that  these  flints  (Mouste- 
rien)  are  of  the  same  form  as  the  obsidian  implements 
which  I  collected  at  Fossil  Lake,  in  Oregon,  with  the 
bones  of  extinct  llamas,  horses,  elephants,  sloth,  etc. 
The  animals  which  accompanied  the  man  of  Spy  are, 
Ccelodonta  antiquitatis  (wooly  rhinoceros),  Equus  ca- 
ballus,  Cervus  elaphus,  Cervus  tarandus,  Bos  primigenius, 
Elephas  primigenius,  Ursus  spelceus,  Meles  taxus,  Hyaena 
spelcea  ;  five  extinct  and  four  existing  species. 

As  the  evidence  now  stands,  the  most  primitive  and 
simian  of  human  races  inhabited  the  Old  World.  No 
trace  of  the  Homo  neanderthalensis  has  been  found  in 
America.  As,  however,  Paleolithic  implements  are 
found  in  all  continents,  we  may  anticipate  that  this  or 
some  similar  species  of  man  will  be  discovered  there 
also.  The  genealogy  of  man  may  be  then  represented 
as  follows  : 


CLASS  &  BRANCH 


Mammalia 


Reptilia 

Batrachia 

Pisces 


ORDER  AND  FAMILY. 

Hominidae 

Simiidae 

Adapidae 

Condylarthra 

Creodonta 

Marsupialia  polyprotodontia 

Monotremata 

Theromora 

Batrachia  Stegocephali 

Teleostomi  Rhipidopterygia 

Elasmobranchii  Ichthyotomi 


GEOL.   SYSTEM 

Plistocene 
Neocene 
Eocene 
Cretaceous 

Jurassic 
Triassic  • 
Carbonic 
Carbonic 


Agnatha 

Cephalochorda       Leptocardii 
Vermes  x 

Coelenterata  * 

Protozoa  * 

1  Subordinate  type  not  specified. 


1 72    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


3.  THE  LAW  OF  THE  UNSPECIALIZED. 

The  facts  cited  in  the  preceding  parts  of  this  chap- 
ter show  that  the  phylogenetic  lines  have  not  been 
continuous,  but  that  they  may  be  represented  by  a 
system  of  dichotomy.  Jn  other  words,  the  point  of 
departure  of  the  progressive  lines  of  one  period  of  time 
has  not  been  from  the  terminal  types  of  the  lines  of 
preceding  ages,  but  from  points  farther  back  in  the 
series.  Thus  it  is  not  the  highly  developed  or  spe- 
cialized plants  which  have  given  origin  to  the  animal 
kingdom,  but  the  lowest  forms  or  Protophyta,  which 
are  not  distinguishable  from  the  Protozoa.  Among 
animals  it  is  not  the  specialized  Arthropoda  or  Mol- 
lusca  which  present  the  closest  affiliations  with  the 
Vertebrata,  but  the  simple  Vermes  or  Tunicata,  from 
which  the  origin  of  the  latter  may  be  traced.  In  the 
Vertebrata  it  is  not  the  higher  fishes  (Actinopterygia) 
which  offer  the  closest  points  of  affinity  to  the  succeed- 
ing batrachian  class,  but  that  more  generalized  type 
of  the  Devonic  period,  the  Rhipidopterygia,  which 
probably  occupies  that  position.  The  modern  types  of 
Batrachia  (Urodela,  Salientia)  have  plainly  not  fur- 
nished the  starting-point  for  the  reptiles,  but  the  an- 
cient order  of  the  Stegocephali,  which  are  also  fish- 
like,  is  evidently  their  source.  The  Reptilia  of  the 
Permian  present  us  with  types  with  fish-like  vertebrae 
(Cotylosauria,  Pelycosauria),  from  which  the  class 
Mammalia  may  be  distinctly  traced.  The  later  reptiles 
diverged  farther  and  farther  from  the  mammalian  type 
with  the  advance  of  geologic  time.  The  same  prin- 
ciple has  been  found  to  be  true  in  tracing  the  history 


PHYLOGENY.  173 

of  the  subdivisions  of  the  great  classes,  in  the  preceding 
section. 

Agassiz  and  Dana  pointed  out  this  fact  in  taxon- 
omy, and  I  expressed  it  as  an  evolutionary  law  under 
the  name  of  the  "Doctrine  of  the  Unspecialized." 
This  describes  the  fact  that  the  highly  developed,  or 
specialized  types  of  one  geologic  period  have  not  been 
the  parents  of  the  types  of  succeeding  periods,  but 
that  the  descent  has  been  derived  from  the  less  spe- 
cialized of  preceding  ages.  No  better  example  of  this 
law  can  be  found  than  man  himself,  who  preserves  in 
his  general  structure  the  type  that  was  prevalent  dur- 
ing the  Eocene  period,  adding  thereto  his  superior 
brain-structure. 

The  validity  of  this  law  is  due  to  the  fact  that  the 
specialized  types  of  all  periods  have  been  generally  in- 
capable of  adaptation  to  the  changed  conditions  which 
characterized  the  advent  of  new  periods.  Changes  of 
climate  and  food  consequent  on  disturbances  of  the 
earth's  crust  have  rendered  existence  impossible  to 
many  plants  and  animals,  and  have  rendered  life  pre- 
carious to  others.  Such  changes  have  been  often  espe- 
cially severe  in  their  effects  on  species  of  large  size, 
which  required  food  in  large  quantities.  The  results 
have  been  degeneracy  or  extinction.  On  the  other 
hand  plants  and  animals  of  unspecialized  habits  have 
survived.  For  instance,  plants  not  especially  restricted 
to  definite  soils,  temperatures,  or  degrees  of  humidity, 
would  survive  changes  in  these  respects  better  than 
those  that  have  been  so  restricted.  Animals  of  om- 
nivorous food-habits  would  survive  where  those  which 
required  special  foods,  would  die.  Species  of  small 
size  would  survive  a  scarcity  of  food,  while  large  ones 
would  perish.  It  is  true,  as  observed  by  Marsh,  that 


174    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

the  lines  of  descent  of  Mammalia  have  originated  or 
been  continued  through  forms  of  small  size.  The 
same  is  true  of  all  other  Vertebrata. 

It  is  not  to  be  inferred  from  the  reality  of  the  law  of 
"the  unspecialized"  that  each  period  has  been  de- 
pendent on  the  simplest  of  preceding  forms  of  life  for 
its  population.  Definite  progress  has  been  made,  and 
highly  specialized  characters  have  been  gradually  de- 
veloped, and  have  passed  successfully  through  the 
vicissitudes  of  geologic  revolutions.  But  these  have 
not  been  the  most  specialized  of  their  respective  ages. 
They  have  presented  a  combination  of  effective  struc- 
ture with  plasticity,  which  has  enabled  them  to  adapt 
themselves  to  changed  conditions. 

In  a  large  number  of  cases  in  each  geologic  age 
forms  have  been  successful  in  the  struggle  for  existence 
through  the  adoption  of  some  mode  of  life  parasitic  on 
other  living  beings.  Such  habits  reduce  the  struggle 
to  a  minimum,  and  the  result  has  been  always  degen- 
eracy. In  other  cases  it  is  to  be  supposed  that  ex- 
tremely favorable  conditions  of  food,  with  absence  of 
enemies,  would  have  occurred,  in  which  the  struggle 
would  have  been  almost  nil.  Degeneracy  would  fol- 
low this  condition  also.  On  the  other  hand,  extreme 
severity  of  the  struggle  cannot  have  been  favorable  to 
propagation  and  survival,  so  that  here  also  we  have  a 
probable  cause  of  degeneracy.  Degeneracy  is  a  fact 
of  evolution,  as  already  remarked,  and  its  character  is 
that  of  an  extreme  specialization,  which  has  been,  like 
an  overperfection  of  structure,  unfavorable  to  sur- 
vival. 

In  general,  then,  it  has  been  the  "golden  mean" 
of  character  which  has  presented  the  most  favorable 
condition  of  survival,  in  the  long  run. 


CHAPTER  III.— PARALLELISM. 


IT  IS  now  generally  recognized  that  the  successive 
types  of  organic  beings  present  characters  which 
are  traversed  in  the  embryonic  life  of  those  which  at- 
tain the  greatest  complexity  of  development,  and  which 
occupy  the  highest  places  in  the  scale  of  life.  This 
fact  was  observed  by  the  early  embryologists,  as  Von 
Baer  and  Agassiz,  who  did  not  admit  its  bearing  on 
the  doctrine  of  evolution.  But  Darwin  and  Spencer 
understood  its  significance,  and  Haeckel,  Hyatt,  and 
the  writer  applied  it  directly  to  the  explanation  of  phy- 
logeny.  At  the  present  time  one  of  the  chief  aims  of 
the  science  of  embryology  is  to  discover  the  record  of 
the  history  of  the  past,  recapitulated  in  the  stages  of 
embryonic  life,  and  to  unravel  the  phylogenesis  of 
plants  and  animals  by  this  method.  The  utility  of 
these  researches  is  attested  by  the  results  which  they 
have  attained,  though  for  obvious  reasons,  these  are 
not  as  definite  and  conclusive  as  those  which  are  de- 
rived from  paleontology.  The  general  conclusion  is 
however  justified,  i.  e.,  that  the  records  of  embryology 
and  paleontology  are  closely  similar,  and  that  any  dis- 
cordance between  them  may  be  explained  on  compre- 
hensible principles. 


176    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

A  number  of  illustrations  of  the  parallelism  be- 
tween taxonomy,  ontogeny,  and  phylogeny  may  now 
be  given. 

i.   PARALLELISM  IN  THE  BRACHIOPODA. 

For  the  following  abstract  I  am  indebted  to  Mr.  C. 
E.  Beecher  of  New  Haven,  whose  excellent  work  in 
this  field  is  well  known. 

The  parallelism  between  the  ontogeny  and  phy- 
logeny in  the  Brachiopoda  has  been  worked  out  in 
numerous  instances.1  To  illustrate  these,  some  more  or 
less  familiar  genera  may  be  taken  as  characteristic  ex- 
amples. 

Lingula  has  been  shown  by  Hall  and  Clarke  (Pa/. 
New  York,  Vol.  VIII.,  1892)  to  have  had  its  inception 
in  the  Ordovician.  In  the  ontogeny  of  both  recent  and 
fossil  forms,  the  first  shelled  stage  has  a  straight  hinge 
line,  nearly  equal  in  length  to  the  width  of  the  shell. 
This  stage  may  be  correlated  with  the  more  ancient 
genus  Paterina  from  the  lowest  Cambrian.  Subsequent 
growth  produces  a  form  resembling  Obolella,  a  Cam- 
brian and  Ordovician  genus.  Then  the  linguloid  type 
of  structure  appears  at  an  adolescent  period,  and  is 
completed  at  maturity.  Thus,  Lingula  has  ontogenetic 
stages  corresponding  to  (i)  Paterina,  (2)  Obolella,  and 
(3)  Lingula,  of  which  the  first  two  occur  as  adult  forms 
in  geological  formations  older  than  any  known  Lin- 
gula. 

Paterina  represents  the  radicle  of  the  brachiopods. 

1C.  E.  Beecher,  "Development  of  the  Brachiopoda,"  Part  I.,  Introduc- 
tion, Amer.  Journ.  Sci.,  Vol,  XLI.,  April,  1891 ;  "  Development  of  the  Brachio- 
poda," Part  II.,  Classification  of  the  Stages  of  Growth  and  Decline,  Amer. 
Jour.  Sci.,  Vol.  XLIV.,  August,  1892  ;  "Development  of  Bilobites,"  Amer. 
Jour.  Sci.,  Vol.  XLII.,  July,  1891 ;  "  Revision  of  the  Families  of  Loop-bearing 
Brachiopoda,"  Trans.  Conn.  Acad.  Sci.,  Vol.  IX.,  May,  1893. 


PARALLELISM.  177 

It  shows  no  separate  stages  of  growth  in  the  shell,  is 
found  in  the  oldest  fossiliferous  rocks,  and  corresponds 
to  the  embryonic  shelled  condition  (protegulum)  of 
other  brachiopods. 

The  genus  Orbiculoidea  of  the  Discinidae  first  ap- 
pears in  the  Ordovician  and  continues  through  the 
Mesozoic.  The  early  stages  in  the  ontogeny  of  an  in- 
dividual are  as  in  Lingula,  first  a  paterina  stage,  fol- 
lowed by  an  obolella  stage.  Then  from  the  mechan- 
ical conditions  of  growth  a  Schizocrania-like  stage 
follows,  and  completed  growth  results  in  Orbiculoidea. 

The  elongate  form  of  the  shell  in  Lingula,  as  well 
as  in  many  other  genera,  is  determined  by  the  length 
of  the  pedicle  and  freedom  of  motion.  The  discinoid 
or  discoid  of  Orbiculoidea  and  Discinisca  among  the 
brachiopods,  and  Anomia  among  pelecypods,  is  deter- 
mined by  the  horizontal  position  of  the  valves,  which 
are  attached  to  an  object  of  support  by  a  more  or  less 
flexible,  very  short  organ,  a  pedicle  or  byssus,  without 
calcareous  cementation.  This  mode  of  growth  is  char- 
acteristic of  all  the  discinoid  genera,  but,  as  already 
shown,  the  early  stages  of  Paleozoic  Orbiculoidea  have 
straight  hinge  lines  and  marginal  beaks,  and  in  the 
adult  stages  of  the  shell  the  beaks  are  usually  subcen- 
tral  and  the  growth  holoperipheral.  This  adult  disci- 
noid form,  which  originated  and  was  acquired  through 
the  conditions  of  fixation  of  the  animal,  has  been  ac- 
celerated in  the  recent  Discinisca,  so  that  it  appears  in 
a  free-swimming  larval  stage.  Thus,  a  character  ac- 
quired in  adolescent  and  adult  stages  of  Paleozoic  spe- 
cies through  the  mechanical  conditions  of  growth,  ap- 
pears by  acceleration  in  larval  stages  of  later  forms 
before  the  assumption  of  the  condition  of  fixation  which 
first  produced  this  character. 


178  PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

The  two  chief  subfamilies  of  the  Terebratellidae 
undergo  complicated  series  of  metamorphoses  in  their 
brachial  structure.  Generic  characters  are  based  upon 
the  form  and  disposition  of  the  brachia  and  their  sup- 
ports. The  highest  genera  in  one  subfamily,  which  is 
austral  in  distribution,  pass  through  stages  correlated 
with  the  adult  structure  in  the  genera  Gwynia,  Cistella, 
Bouchardia,  Megerlina,  Magas,  Magasell,  and  Terebra- 
tella,  and  reach  their  final  development  in  Magellania 
and  Neothyris.  The  higher  genera  in  another  subfam- 
ily, boreal  in  distribution,  pass  through  metamorphoses 
correlated  with  the  adult  structures  of  Gwynia,  Cistella, 
Platidia,  Ismenia,  Miihlfeldtia,  Terebratalia,  and  Dal- 
lina.  The  first  two  stages  in  both  subfamilies  are  re- 
lated in  the  same  manner  to  Gwynia  and  Cistella.  The 
subsequent  stages  are  different  except  the  last  two,  so 
that  the  Magellania  structure  is  similar  in  all  respects 
to  the  Dallina  structure,  and  Terebratella  is  like  Tere- 
bratalia. Therefore  Magellania  and  Terebratella  are 
respectively  the  exact  morphological  equivalent  to,  or 
are  in  exact  parallelism  with  Dallina  and  Terebratalia. 

The  stages  of  growth  of  the  genera  belonging  to 
the  two  subfamilies  Dallininae  and  Magellanimae  are 
further  correlated  in  the  accompanying  tables. 

The  simplest  genus  Gwynia,  as  far  as  known,  passes 
through  no  brachial  metamorphoses,  and  has  the  same 
structure  throughout  the  adolescent  period,  up  to  and 
including  the  mature  condition.  In  the  ontogeny  of 
Cistella  the  gwyniform  stage,  through  acceleration,  has 
become  a  larval  condition.  In  Platidia,  the  cistelliform 
structure  is  accelerated  to  the  immature  period,  and 
in  Ismenia  (representing  an  ismeniform  type- of  struc- 
ture in  the  higher  genera),  the  gwyniform  and  cistelli- 
form stages  are  larval,  and  the  platidiform  represents 


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i8o    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

an  adolescent  condition.  Similar  comparisons  may  be 
made  in  the  other  genera.  Progressively  through  each 
series,  the  adult  structure  of  any  genus  forms  the  last 
immature  stage  of  the  next  higher,  until  the  highest 
member  in  its  ontogeny  represents  serially,  in  its  stages 
of  growth,  all  the  adult  structures,  with  the  larval  and 
immature  stages  of  the  simpler  genera.  It  is  evident 
that  in  the  identification  of  specimens  belonging  to 
the  Terebratellidae,  whether  recent  or  fossil,  the  strict 
specific  characters  must  be  given  first  consideration. 
Species,  therefore,  must  be  based  upon  surface  orna- 
ments, form,  and  color,  within  certain  limits,  and  gen- 
era only  upon  structural  features  developed  through  a 
definite  series  of  changes;  the  results  of  which  are  per- 
manent in  individuals  evidently  fully  adult. 

In  each  line  of  progression  in  the  Terebratellidae, 
the  acceleration  of  the  period  of  reproduction,  by  the 
influence  of  environment,  threw  off  genera  which  did 
not  go  through  the  complete  series  of  metamorphoses, 
but  are  otherwise  fully  adult,  and  even  may  show  re- 
versional  tendencies  due  to  old  age  ;  so  that  nearly 
every  stage  passed  through  by  the  higher  genera  has 
a  fixed  representative  in  a  lower  genus.  Moreover, 
the  lower  genera  are  not  merely  equivalent  to,  or  in 
exact  parallelism  with  the  early  stages  of  the  higher, 
but  they  express  a  permanent  type  of  structure,  as  far 
as  these  genera  are  concerned,  and  after  reaching  ma- 
turity do  not  show  a  tendency  to  attain  higher  phases 
of  development,  but  thicken  the  shell  and  cardinal  pro- 
cess, absorb  the  deltidial  plates,  and  exhibit  all  the 
evidences  of  senility. 


182    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


2.   PARALLELISM  IN  THE  CEPHALOPODA. 

Among  Mollusca  it  is  well  known  that  the  Cepha- 
lopoda form  a  number  of  series  of  remarkable  regular- 
ity, the  advance  being,  in  the  first  place,  in  the  com- 
plication of  the  folds  of  the  external  margins  of  the 
septa,  and,  in  the  second  place,  in  the  degree  of  invo- 
lution of  one  or  both  extremities  of  the  shell  to  the 
spiral  ;  third,  in  the  position  of  the  siphon. 

Alpheus  Hyatt,  in  an  important  essay  on  this  sub- 
ject,1 points  out  that  the  less  complex  forms  are  in 
many  cases  identical  with  the  undeveloped  conditions 
of  the  more  complex.  He  says:  "  There  is  a  direct 
connection  between  the  position  of  a  shell,  in  the  com- 
pleted cycle  of  the  life  of  this  order,  and  its  own  de- 
velopment. Those  shells  occupying  the  extremes  of 
the  cycle"  (in  time),  "the  polar  forms,  being  more 
embryonic  than  the  intermediate  forms.  The  first 
epoch  of  the  order  is  especially  the  era  of  rounded, 
and,  in  the  majority  of  the  species,  of  unornamented 
shells  with  simple  septa ;  the  second  is  the  era  of  or- 
namentation, and  the  septa  are  steadily  complicating; 
in  the  third  the  complication  of  the  septa,  the  orna- 
mentation, and  the  number  of  species,  about  twice 
that  of  any  other  epoch,  all  combine  to  make  it  the 
zenith  of  development  in  the  order  ;  the  fourth  is  dis- 
tinguishable from  all  the  preceding  as  the  era  of  re- 
trogression in  the  form,  and  partially  in  the  septa. 

"The  four  periods  of  the  individual  are  similarly 
arranged,  and  have  comparable  characteristics.  As 

\Metnoirs  of  the  Boston  Society  for  Natural  History,  1866,  p.  193.  Hyatt 
was  followed  by  WQrtenberger  in  Ausland,  1873,  who  entirely  confirmed  his 
conclusions. 


PARALLELISM.  183 

has  been  previously  stated,  the  first  is  rounded  and 
smooth,  with  simple  septa ;  the  second  tuberculated, 
and  the  septa  more  complicated;  the  third  was  the 
only  one  in  which  the  septa,  form,  and  ornamentation 
simultaneously  attained  the  climax  of  individual  com- 
plication; the  fourth,  when  amounting  to  anything 
more  important  than  the  loss  of  a  few  ornaments,  was 
marked  by  a  retrogression  of  the  whorl  to  a  more  tabu- 
lar aspect,  and  by  the  partial  degradation  of  the  septa." 

I  am  indebted  to  Professor  Hyatt  for  the  following 
more  detailed  account  of  the  results  of  his  researches 
in  this  interesting  field.  The  evidence  as  to  the  na- 
ture of  evolution  derived  from  the  Cephalopoda  is  more 
complete  than  that  obtained  from  any  other  source. 

"Every  group  of  nautiloids  passes  through,  during 
its  evolution  in  time,  either  a  part  or  the  whole  of  a 
certain  series  of  changes.  These  modifications  con- 
sist :  first,  of  a  straight  or  nearly  straight  cone,  ortho- 
ceran ;  second,  a  curved  cone,  cyrtoceran ;  third,  a 
coiled  cone,  gyroceran,  which  does  not  come  in  con- 
tact at  any  point;  fourth,  a  coiled  cone,  nautilian,  which 
does  come  in  contact  at  the  termination  of  the  first  vo- 
lution and  then  during  further  growth  remains  in  about 
the  same  condition,  all  of  the  internal  whorls  being 
visible  as  in  a  flat  coil  of  rope  ;  fifth,  a  coiled  cone, 
involute-nautilian,  which  also  comes  in  contact  like 
the  fourth  but  then  the  whorl  growing  with  greater 
rapidity  spreads  internally,  covering  up  more  or  less 
of  the  internal  volutions  sometimes  to  such  an  extent 
that  even  the  centre  is  concealed  from  view.  The  ex- 
amples which  I  have  myself  seen  of  the  fifth  kind  range 
from  the  Silurian  to  the  Nautili  of  the  existing  fauna, 
some  being  present  in  every  period,  and  of  other  kinds, 
the  first,  second,  and  third  kinds  die  out  gradually, 


184    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

diminishing  in  the  Devonian  and  Carboniferous  and 
ultimately  ceasing  their  existence  altogether  in  the 
Trias.  The  fourth  ceases  in  the  Cretaceous,  and  the 
fifth  alone  survives  in  the  Tertiaries  and  is  still  living 
in  the  Nautilus  umbilicatus  and  pompilus,  and  two  other 
species. 

"Wherever  found,  the  young  of  shells  of  the  fifth 
kind  are  at  first  orthoceran  or  cyrtoceran  like  the  first 
and  second  kind,  then  gyroceran  in  curvature  like  the 
third  class,  and  then  they  become  more  or  less  rapidly 
nautilian  like  the  fourth  class  in  succeeding  stages.  In 
Silurian,  Devonian,  and  Carboniferous  forms  this  suc- 
cession is  so  marked  that  about  all  of  the  young  shells 
of  the  fifth  class  may  be  described  as  palingenetic, 
that  is  as  cyrtoceran,  gyroceran,  nautilian,  and  then 
involute-nautilian  in  their  individual  or  ontogenetic 
development.  In  the  Trias,  Jura,  Cretaceous,  Ter- 
tiary, and  present,  as  the  fifth  class  increases  in  num- 
bers, there  is  a  decided  tendency  to  shorten  and  su- 
persede the  gyroceran  or  third  stage  and  introduce  the 
fourth  kind  or  the  tendency  to  spread  by  growth  in- 
wards, at  earlier  stages. 

"The  characteristics  of  the  sutures  are  correlative 
with  these  stages  of  development,  and  it  may  be  said 
in  a  general  way,  that  all  other  characteristics  corre- 
late more  or  less  when  studied  comparatively  in  dif- 
ferent series  with  the  differences  in  the  curvature  and 
coiling  of  the  whorls.  The  curvature  and  amount  of 
involution  is  therefore  the  most  important  single  char- 
acteristic of  the  nautiloids,  so  far  as  the  comparative 
study  of  change  by  evolution  is  concerned,  whether 
the  whole  order  be  considered  statistically  as  above, 
i.  e.  with  reference  to  the  existence  or  non-existence 
of  certain  forms  orthoceran,  cyrtoceran,  etc.,  or  gen- 


PARALLELISM.  185 

etically,  i.  e.  with  sole  regard  to  the  evolution  of  dis- 
tinct series  which  may  be  traced  from  their  origin  to 
their  termination  in  time. 

"Of  these  last  there  are  some  in  every  period  trace- 
able with  more  or  less  completeness  by  gradations  of 
adults  back  to  orthoceran  or  cyrtoceran  ancestors.  Of 
these  series  of  adults,  some  pass  through  only  the  or- 
thoceran and  cyrtoceran  modifications,  others  have 
the  orthoceran,  cyrtoceran,  gyroceran,  and  nautilian, 
but  those  having  the  latter  and  the  nautilian- involute 
are  of  extreme  rarity  until  the  Carboniferous  is  reached. 
After  this  the  nautilian  shells  begin  to  predominate  in 
every  series,  ultimately  becoming  the  sole  representa- 
tives of  genetic  series. 

"Such  series  are,  of  course,  frequently  so  closely 
parallel  that  it  is  possible  to  follow  them,  and  show 
they  are  distinct  only  by  means  of  certain  genetic  char- 
acters, the  apertures,  the  structure  of  the  siphuncle, 
the  sutures  and  septa,  and  sometimes,  although  very 
rarely,  all  of  these  internal  characters  may  show  dif- 
ferences peculiar  to  some  one  genetic  series  in  which 
the  regular  gamut  of  forms  is  passed  through  in  the 
usual  succession.  Neglect  of  the  comparative  study 
of  the  stages  of  development  and  decline,  and  of  the 
obvious  parallelisms  between  these  and  adults  of  an- 
cestral forms,  have  caused  naturalists,  notably  Bar- 
rande,  to  make  artificial  classifications  in  which  about 
all  straight  forms,  with  the  exception  of  some  in  which 
the  siphuncles  were  notably  distinct  to  be  classed  as 
Orthoceras,  most  of  second  kind  as  Cyrtoceras,  most 
of  the  third  kind  as  Gyroceras,  most  of  the  fourth  and 
fifth  kinds  as  Nautilus. 

"To  such  authors  the  involute-nautilian  forms  of 
the  Silurian  and  the  existing  fauna  were  considered  to 


i86    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

be  only  specifically  distinct,  although  any  prolonged 
study  and  comparison  of  the  young  would  have  shown 
that  they  were  widely  separated  in  development  and 
really  only  morphic  equivalents  evolved  from  entirely 
distinct  ancestors. 

"A  good  example  of  this  is  the  Eudoceratidae1  in- 
cluding the  Silurian  and  Devonian  Eudoceras  and  Trip- 
teroceras,  and  probably  gyroceran  form  Edaphoceras 
of  the  Carboniferous  and  the  close-coiled  nautilian 
shells  of  Endolobus  of  the  Carboniferous.  The  pe- 
culiar forms  of  this  series  and  their  remarkable  sutures 
enable  the  observer  to  follow  the  line  both  in  the  grada- 
tions of  the  adults  and  by  means  of  the  parallelisms 
of  the  development. 

"Another  good  series  easily  distinguished  by  the  re- 
markable sculpture  of  the  shells  is  Zittelloceras  of  the 
Silurian  with  cyrtoceran  forms,  and  the  gyroceran  and 
nautilian  Halloceras  of  the  Devonian. 

"One  of  the  best  is  Thoraceras,  a  rough  spinous 
cone  of  the  Silurian,  Devonian,  and  Carboniferous, 
which  has  straight  and  cyrtoceran  shells ;  the  gyroceran 
Triboloceras  of  the  Carboniferous,  and  the  nautilian 
shells  of  Vestinautilus  and  its  allies  in  the  same  period. 

"There  is  no  possible  explanation  of  the  parallel- 
isms of  development  of  these  nautilian  shells  and  the 
adult  stages  of  others  except  heredity  in  the  same  gen- 
etic series.  It  is  useless  to  waste  time  in  discussion 
unless  the  facts  are  specifically  denied  after  having 
been  properly  reexamined. 

"When  the  ammonoids  are  taken  up,  it  is  easy  to 
demonstrate2  by  the  study  of  the  young  of  the  Gonia- 

1 "  Genera  of  Fossil  Cephalopods,"  Proc.  Bost.  Soc.  Nat.  Hist,,  p.  287. 
2  See  "  Genera  of  Fossil  Cephalopods,"  Proc.  Bost,  Soc.  Nat.  Hist.,  XXII., 
1883,  p.  303. 


PARALLELISM.  187 

titinae  that  they  had  straight  forms  among  their  ances- 
tors and  that  these  forms  have  a  central  siphuncle  and 
suture  as  among  nautiloids.  The  Devonian  Goniati- 
tinae  and  some  of  the  Carboniferous  forms  had  also 
gyroceran  forms  and  loosely  coiled  nautilian  forms,  in- 
dicating an  ancestry  with  similar  cones,  but  at  these 
stages  the  siphuncle  is  invariably  ventral  as  in  the 
adults.  The  young  of  all  of  the  Ammonitinae,  however 
involute  the  shell  may  afterwards  become,  have  an  in- 
variably straight  or  curved  cyrtoceran  cone  in  the 
apical  part,  and  when  they  come  in  contact  by  growth, 
the  first  whorl  or  whorls  are  equally  invariably  open 
coils  like  the  coils  of  the  fourth  grade  in  nautiloids. 
The  fifth  kind  of  shell,  the  involute-nautilian,  follows 
in  precisely  similar  succession  to  what  it  does  in  the 
ontogeny  of  nautiloids.  Farther  than  this  the  degree 
of  involution  increases  according  to  the  species,  with 
age,  and  the  amount  of  this  involution  is  often  an  im- 
portant part  of  the  specific  diagnosis. 

"Among  Ammonitinae  one  finds  at  once  that  there 
are  no  orthoceran  or  cyrtoceran  shells  except  among 
the  large  group  designated  by  the  author  as  Bactrites. 
This  genus  begins  early  in  the  Silurian  with  shells  that 
are  not  distinguishable  from  true  Orthoceras  except 
by  having  the  siphuncle  in  adults  and  later  stages 
close  to  the  venter.  Some  of  these  forms  have  no 
bulb  or  protoconch  and  have  a  large  scar  on  the  apex 
as  in  true  Orthoceras,  others  have  a  calcareous  bulb 
or  protoconch  on  the  apex  as  in  true  Ammonitinae. 
There  are  also  open  or  gyroceran  shells  in  the  adults 
of  the  genus  Mimoceras  which  are  repeated  in  the 
young  of  Anarcestes  and  other  genera  of  Goniatitinae 
figured  in  my  'Embryology  of  Fossil  Cephalopods.'1 

1  Bull.  Mus.  Comp.  Zodl.,  III. 


1 88    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

The  shells  of  the  Ammonitinae,  however,  are  of  the 
fourth  and  fifth  kinds  almost  exclusively,  and  in  fol- 
lowing out  the  separate  genetic  series  one  has  to  dis- 
tinguish the  progressive  gradations  by  means  of  the 
greater  or  less  amount  of  involution  even  in  the  Go- 
niatitinae  of  the  Devonian  and  Carboniferous. 

"There  are  also  some  very  remarkable  facts  show- 
ing that  the  coiling  is  closer  in  the  Mesozoic  than  in  the 
Paleozoic  forms  as  a  matter  of  hereditary  derivation. 
The  young  of  the  Silurian  and  Devonian  forms  have 
the  open,  slowly  coiling  whorls  figured  by  Sandberger 
and  Barrande  and  repeated  by  myself  as  referred  to 
above,  but  the  young  of  all  Mesozoic  forms  are  close 
coiled  so  far  as  known.  This  is  shown  in  the  centre 
of  the  umbilicus  by  the  perforation  or  central  opening 
which  is  extremely  large  in  most  of  the  Paleozoic  Go- 
nititinae  but  becomes  almost  obliterated  in  the  true 
Ammonitinae  of  the  Jura. 

"In  tracing  parallels  between  development  of  the 
individual  and  the  series  among  Ammonitinae  it  has 
been  found  by  Branco  and  the  author,  that  in  orna- 
mented shells  the  young  are  first  like  a  nautilus  in  the 
sutures,  then  have  a  goniatitic  stage  like  the  first  rep- 
resentatives of  the  order  of  ammonoids  in  the  Paleo- 
zoic, and  that  during  these  stages  it  is  invariably 
smooth  and  similar  in  general  form  to  these  same  an- 
cestors. After  this  nepionic  stage  is  passed  through 
the  sutures  and  the  characteristics  alter  with  greater 
or  less  rapidity,  but  the  stages  show  decisive  parallel 
isms  with  the  immediate  ancestors  of  the  same  genetic 
series.  Some  of  the  best  examples  of  palingenetic  de- 
velopment of  this  kind,  where  the  later  stages  of  growth 
present  parallels  with  proximate  ancestors,  are  cited  in 


PARALLELISM.  189 

my  «  Genesis  of  the  Arietidae  ' 1  and  others  have  been 
given  by  Buckman  and  Wiirtenburger. 

"Some  of  the  most  remarkable  occur  in  the  least 
expected  quarters.  As  usual,  when  one  has  a  true  law, 
it  leads  him  into  conclusions  that  are,  perhaps,  more 
surprising  to  himself  than  to  his  readers,  or  to  any 
subsequent  investigator.  This  was  certainly  my  own 
case  in  being  led  to  recognise  the  perfect  examples  of 
parallelisms  in  retrogressive  series.  Quenstedt  and 
all  students  since  his  time  agree  that  the  so-called 
genera  Crioceras,  Hamites,  Ancyloceras,  Baculites, 
forms  that  are  successively  more  and  more  uncoiled 
until  in  Baculites  they  are  absolutely  straight  cones, 
were  derived  from  normal,  close-coiled,  involute-nau- 
tilian  shells  of  the  Ammonitinae.  Their  young  have 
been  repeatedly  shown  to  be  close-coiled  and  they 
grade  into  the  normal  progressive  shells  by  all  of  their 
adult  characters. 

"The  ultimate  fact  in  this  demonstration  has  been 
added  by  Dr.  Amos  Brown  in  the  discovery  of  a  close 
coiled  nepionic  stage  in  the  straight  Baculites  of  the 
Cretaceous,  the  only  form  whose  development  had  not 
been  ascertained  and  whose  exact  relations  had  not 
been  determined. 

"It  is  now  admitted  by  all  students  of  Ammonitinae 
that  these  retrogressive  groups  are  not  true  genera; 
but  that  as  first  demonstrated  by  Quenstedt,  Baculites, 
Crioceras,  etc.,  are  retrogressive  stages  in  the  evolu- 
tion of  distinct  genetic  series  and  that  they  do  not  ex- 
ist as  natural  groups  of  species.  In  other  words,  dif- 
ferent genetic  series  of  the  Ammonitinae  die  out  by 
passing  through  a  series  of  modifications  which  are 
parallel  and  which  are  just  the  reverse  of  the  parallel 

1  Smitlison.  Contrib.,  673,  p.  41  et  seq. 


igo    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

series  of  the  orthoceran,  cyrtoceran,  gyroceran  shells 
with  which  each  distinct  complete  genetic  series  of 
nautiloids  arose  in  time. 

"While  the  nautiloids  coil  up  in  their  progressive 
evolution  and  the  Ammonitinae  increase  this  coiling  up 
tendency  in  the  primitive  and  progressive  forms  of 
each  genetic  series,  the  latter  in  becoming  retrogres- 
sive reverse  the  processes  of  progressive  evolution. 
They  become  more  and  more  uncoiled,  each  complete 
retrogressive  series  ending  with  a  straight  cone.  All 
other  characters  correlate  with  this  uncoiling  and  in  a 
general  way  may  be  said  to  degenerate  in  greater  or 
less  proportion  to  the  amount  of  the  uncoiling.  To 
make  this  extraordinary  picture  complete  it  is  only 
necessary  to  add  that  these  retrogressive  series  followed 
out  to  their  ultimate  development  are  distinctly  parallel 
with  changes  or  stages  of  modification  taking  place  in 
the  senile  stages  of  individuals  of  the  same  genetic 
group. 

"In  old  age  the  highly  ornamented  shell  gradually 
parts  with  its  spines  and  other  ornaments,  the  whorls 
slowly  diminish,  the  involution  decreases  and  even- 
tually in  extreme  age  it  becomes  separated  from  the 
spiral  and  completely  rounded  and  smooth.  The  aper- 
ture becomes  correlatively  modified,  and  also  the  su- 
tures. If  an  old  ammonite  could  have  its  life  pro- 
longed, it  would  become  Baculites,  and  the  full-grown 
part  of  the  shell  would,  in  some  forms  of  Lytoceratinae 
be  very  similar  to  the  minute  nepionic  shell  of  the  Ba- 
culites as  described  and  figured  by  Dr.  Brown.  If  now 
the  coiled  adult  part  of  this  imaginary  shell  were  broken 
off  and  lost,  the  straight  senile  fragment  would  be  re- 
ferred to  the  old  genus  Baculites.  The  morphic  char- 
acters of  the  gerontic  or  old-age  stage  of  ontogeny  are 


PARALLELISM.  191 

therefore  parallel  with  the  forms  evolved  in  the  para- 
plastic  or  retrogressive  stage  of  evolution  of  the  phy- 
lum. In  other  words,  the  morphic  modifications  which 
may  occur  as  permanent,  specific,  and  generic  charac- 
ters in  the  adults  of  retrogressive  descendants  of  any 
progressive  individuals  may  be  predicted  from  the 
study  of  the  similar  changes  that  take  place  in  the 
senile  stages  of  the  progressive  individuals.  As  it  has 
been  stated  by  the  writer  on  several  occasions,  the 
embryonic,  nepionic,  and  later  stages  of  development 
up  to  the  adult  repeat  with  greater  or  less  clearness  in 
proportion  to  their  removal  in  time  and  organization 
from  the  point  of  the  origin  of  the  genetic  group  to 
which  they  belong  the  permanent  characteristic  of 
their  ancestors  ;  the  adult  gives  the  existing  essential 
differentials  acquired  by  its  own  species,  genus,  and 
group,  being  the  index  according  to  the  time  of  its  oc- 
currence of  the  progression  or  retrogression  of  its 
group;  the  old,  in  its  invariably  retrogressive  course, 
indicates  the  path  that  must  be  followed  by  degraded 
series  after  the  acme  of  the  group  to  which  the  indi- 
vidual belongs  has  been  reached.  This,  of  course,  is 
a  generalized  statement  of  the  correlations  of  the  on- 
togenic  cycle  and  the  phylocycle  when  they  occur  as 
in  the  Ammonitinae,  but  it  will  be  found  eventually 
that  this  law  is  true  of  all  animals  to  some  degree.  It 
is  obvious  from  all  past  experience  that  every  law  of 
correlation  of  structures  cannot  be  true  in  any  one 
group  without  being  found  more  or  less  in  all  organ- 
isms. I  have  therefore  ventured  upon  the  basis  of 
this  and  Beecher's,  Clarke's,  and  Schuchert's  re- 
searches among  Brachiopoda,  corals,  and  trilobites, 
Dr.  Jackson's  among  pelecypods,  and  after  the  con- 
firmations by  the  independent  researches  of  Wurten- 


i92    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

burger  and  Buckman  among  Ammonitinae,  and  those 
of  Bather  among  crinoids,  to  designate  the  complete 
study  of  the  correlations  of  the  ontocycle  and  phylo- 
cycle  as  Bioplastology.  Bioplastology  is  easily  sepa- 
rable from  the  study  of  growth,  and  from  that  of  hered- 
ity, for  which  last  I  have  proposed  the  term  Genesi- 
ology,1  and  from  that  of  Ctetology  or  the  study  of  the 
origin  of  acquired  characteristics.  By  properly  denn- 
ing these  different  branches  of  research  it  is  practicable 
to  see  that  bioplastology  includes  the  results  of  the  ac- 
tion of  growth,  the  laws  of  growth,  as  well  as  those  of 
genesiology  and  ctetology,  but  has  a  field  entirely  dis- 
tinct from  all  of  these  in  so  far  as  it  deals  essentially 
with  the  study  of  parallelism  in  all  its  phases. " 

The  parallelism  of  the  gyroceras  with  an  early  stage 
of  all  coiled  Cephalopoda  is  represented  in  Fig.  119 
page  410,  as  illustrative  of  the  inheritance  of  an  ac- 
quired character. 


3.  PARALLELISM  IN  THE  VERTEBRATA. 

Parallels  between  the  ontogeny  and  phylogeny  are 
well  known  in  the  Vertebrata.  The  primary  relations 
of  the  Vertebrata  are  discernible  in  the  successive 
types  of  structure  of  the  nervous  system,  and  of  the 
skeleton,  but  most  clearly  in  those  presented  by  the 
circulatory  system.  It  is  well  known  that  the  central 
organ — the  heart,  is,  in  the  amphioxus,  a  straight 
tube.  In  the  next  higher  group,  the  Marsipobranchii 
(lampreys),  it  is  a  bent  tube,  with  a  constriction  which 
divides  it  into  two  chambers.  In  the  Pisces  (fishes) 
the  heart  is  composed  of  two  chambers  related  to  each 
other  in  a  reversed  longitudinal  direction.  In  the  Ba- 

1  See  Proceedings  of  the  Boston  Society  of  Natural  History,  1893,  p.  59. 


PARALLELISM.  193 

trachia  and  Reptilia  the  cephalad  (auricular)  division 
is  divided  into  two  chambers  by  a  septum ;  while  in 
the  birds  and  Mammalia  the  caudad  division  (ventricle) 
is  also  so  divided,  making  four  chambers  in  all. 

The  sources  of  the  great  vessels  which  distribute 
the  blood  to  the  body  and  return  it  to  the  heart,  dis- 
play the  same  successional  relation  of  types.  In 
the  Acrania  (amphioxus),  the  Marsipobranchii,  and 
most  of  the  fishes,  the  vessel  (truncus  communis) 
which  receives  the  blood  from  the  central  organ,  gives 
off  several  branches  on  each  side,  which  are  distributed 
to  skeletal  bars  or  arches  which  are  in  immediate  con- 
tact with  water,  which  aerates  the  blood.  They  then 
return,  and,  first  sending  the  carotids  anteriorly,  unite 
dorsad  to  the  heart,  and  form  the  aorta  posteriorly.  In 
the  Batrachia,  where  aerial  respiration  succeeds  to  an 
aquatic  one  during  the  life  of  the  animal,  the  number 
of  the  vessels  contributing  to  form  the  aorta  is  re 
duced  from  five  to  three  in  the  sucessive  types.  One 
of  the  arches  is  aborted  as  an  arch,  and  sends  the  cir- 
culating fluid  to  the  modified  swim-bladder  of  the  fish, 
or  lung,  where  it  is  aerated.  This  aerated  blood  is 
returned  to  the  heart  with  non-aerated  blood  from 
other  organs,  and  the  mixture  is  sent  throughout  the 
body.  In  the  reptiles  we  have  essentially  the  same 
system,  but  the  aorta-origins  are  reduced  to  two,  and 
one,  on  each  side.  Next  a  division  of  the  truncus  com- 
munis ensues,  which  corresponds  functionally  with 
that  in  the  ventricle,  so  that  the  impure  blood  from 
one  auricle  is  sent  into  the  ventricle  (right)  which  com- 
municates with  the  lung ;  and  the  aerated  blood  is 
then  returned  to  the  other  auricle,  which  pours  its 
contents  into  the  left  auricle,  which  drives  it  into  the 
aorta,  and  thus  throughout  the  body.  Thus  pure  or 


Fig.  49. — Circulatory  systems;    1-2,  fish;    3-4,   batrachian;    5,  reptile;    6,  bird;    all 
from  Gegenbaur.     Figs.  7-8,  human  foetus,  from  His. 


PARALLELISM.  195 

aerated  blood  is  distributed  to  the  organs,  and  all  but 
one  of  the  old  roots  of  the  aorta  have  ceased  to  function 
as  such. 

This  evolutionary  succession  is  preserved  with  much 
fidelity  in  the  ontogeny  of  the  respective  classes  of 
Vertebrata.  The  representatives  of  each  class  pass 
through  the  stages  which  are  permanent  in  the  classes 
below  them  in  the  series.  The  Mammalia,  as  the 
highest  class,  pass  through  all  the  stages.  (Fig.  49.) 
This  series  coincides  also  with  phylogenetic  succes- 
sion. The  order  of  appearance  in  time  of  the  Verte- 
brata is,  first  Agnatha,  then  Pisces,  Batrachia,  Rep- 
tilia,  and  Mammalia. 

In  all  the  details  of  structure  the  same  relation 
may  be  observed.  Referring  to  the  illustrations  of 
phylogeny  and  variation  of  character  described  in  the 
preceding  pages,  many  of  the  characters  definitive  of 
natural  divisions  have  been  observed  to  appear  in  the 
course  of  the  embryonic  life  of  those  types  which  pos- 
sess them.  Those  of  greater  systematic  significance 
appear  earlier,  and  those  of  less  importance  in  a  tax- 
onomic  sense,  later.  I  select  some  illustrations  of  this 
principle. 

I  have  shown  that  the  primitive  type  of  superior 
molar  in  the  placental  Mammalia  is  tritubercular,  the 
fourth  tubercle  being  added  internally  and  posteriorly 
in  the  later  forms.  Dr.  Taeker  has  recently  observed 
that  in  the  development  of  the  superior  molars  in  the 
horse,  at  an  early  stage  the  crown  is  tritubercular,  and 
that  the  fourth  cusp  or  hypocone  is  subsequently  added, 
as  in  the  phylogenetic  history.  As  the  horse  presents 
the  most  complex  molar  among  Mammalia,  this  sur- 
vival of  the  record  is  interesting. 

In  the  Artiodactyla  and   Edentata  which   lack  su- 


196    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

perior  incisor  teeth,  rudiments  of  them  can  be  found 
in  the  early  stages.  We  now  know  early  extinct  forms 
of  both  of  these  types  where  these  teeth  are  permanent 
throughout  life.  In  the  toothless  whalebone  whales 
the  same  phenomenon  has  been  observed. 

It  is  well  known  that  the  highest  deer  (Cervidae) 
add  an  antler  to  the  simple  spike  horn  in  the  third 
year,  and  an  additional  antler  with  each  successive 
year  for  several  years.  Also  they  develop  a  basal  snag 
of  the  antler  (see  Cuvier,  Ossem.  Fossiles  ;  Gray,  Catal. 
Brit.  Mus.)  at  the  third  year.  Now  a  majority  of  those 
of  the  New  World  (genera  Cariacus,  Coassus)  never 
develop  it  except  in  "abnormal"  cases  in  the  most 
vigorous  maturity  of  the  most  northern  Cariacus  (C. 
virginianus);  while  the  South  American  Coassus  retains 
to  adult  age  the  simple  horn  of  the  second  year  of 
Cervus. 

Among  the  higher  Cervidae,  Rusa  and  Axis  never 
assume  characters  beyond  an  equivalent  of  the  fourth 
year  of  Cervus.  In  Dama  the  characters  are  on  the 
other  hand  assumed  more  rapidly  than  in  Cervus,  its 
third  year  corresponding  to  the  fourth  of  the  latter, 
and  the  development  in  after  years  of  a  broad  plate  of 
bone,  with  points,  being  substituted  for  the  addition 
ot  the  corresponding  snags,  thus  commencing  another 
series. 

Returning  to  the  American  deer,  we  have  Blasto- 
cerus,  whose  antlers  are  identical  with  those  of  the 
fourth  year  of  Cariacus. 

The  oldest  known  deer  (Palaeomeryx)  have  no 
horns,  or  they  are  undivided. 

Among  Batrachia  excellent  illustrations  are  fur- 
nished by  the  two  series  of  Salientia,  the  Arcifera  and 
the  Firmisternia. 


PARALLELISM. 


197 


The'firmisternial  structure  is  a  modification  of  the 
arciferous,  which  comes  later  in  the  history  of  growth, 
and  probably  also  in  geological  time.  During  the 
early  stages  the  Firmisternia  have  the  movable  shoul- 


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der  girdle  which  characterizes  those  of  the  arciferous 
division,  the  consolidation  constituting  a  modification 
superadded  in  attaining  maturity.  Furthermore,  young 
Salientia  are  toothless,  and  one  section  of  the  species 
of  Arcifera  never  acquire  teeth.  In  these  (the  Bu- 


ig8    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


fonidae)  we  have  a  group  which  is  imperfect  in  two 
points  instead  of  one. 

The  genera  of  these  salientian  suborders  exhibited 
on  a  preceding  page  as  forming  indentical  series  in  five 
different  families  (pp.  66-67)  are  related  to  each  other 
as  developmental  stages  in  the  history  of  the  genera 
that  attain  the  extreme  development  on  each  line. 
For  example  we  select  the  family  Hylidae  of*  which 
the  terminal  genus  is  Trachycephalus.  Nearly  allied 


Fig.  51. — Shoulder  girdles  of  Anura  ;  a,  of  the  arciferous  type  (Phyllomedusa 
bicolor)  ;  b,  Rana  temporaria,  tadpole  with  budding  limbs;  c,  do.,  adult,  firrais- 
ternial  type  ;  b  and  c  from  Parker. 

to  it  is  the  genus  Osteocephalus,  which  differs  in  the 
normal  exostosis  of  the  cranium  not  involving  the 
derm,  as  it  does  in  the  former.  Close  to  this  is  Scy- 
topis,  where  the  fully  ossified  cranium  is  not  covered 
by  an  exostosis.  Next  below  Scytopis  is  Hyla,  where 
the  upper  surface  of  the  cranium  is  not  ossified  at  all, 
but  is  a  membranous  roof  over  a  great  fontanelle.  Still 
more  imperfect  is  Hylella,  which  differs  from  Hyla  in 
the  absence  of  vomerine  teeth.  Now,  the  genus  Trachy- 
cephalus, after  losing  its  tail  and  branchiae,  possesses 


PARALLELISM.  199 

all  the  characters  possessed  by  the  genera  Hylella 
and  Hyla,  either  at  or  just  before  the  mature  state  of 
the  latter,  as  the  ethmoid  bone  is  not  always  ossified 
in  advance  of  the  parietals.  It  soon,  however,  becomes 
a  Scytopis,  next  an  Osteocephalus,  and  finally  a  Tra- 
chycephalus.  It  belongs  successively  to  these  genera, 
for  an  exhaustive  anatomical  examination  has  failed 
to  reveal  any  characters  by  which,  during  these  stages, 
it  could  be  distinguished  from  these  genera.  The  same 
succession  in  development  of  the  genera  of  the  other 
families  is  well  known,  the  genus  Otaspis  of  the  Bu- 
fonidse  attaining  a  point  beyond  any  of  the  others,  in 
the  enclosure  of  its  membranum  tympani  posteriorly 
by  dermoossification. 

Finally  reaching  in  our  review  the  relations  of  spe- 
cific characters,  the  readers  will  call  to  mind  that  the 
species  of  the  lacertilian  genus  Cnemidophorus  (page 
41)  are  either  striped,  spotted,  or  cross-banded,  and 
that  the  Lacerta  muralis  agrees  with  them  in  this  re- 
spect. It  was  also  shown  that  the  young  of  all  the 
species  are  striped,  and  that  the  cross-banded  forms 
pass  through  not  only  a  striped,  but  an  intermediate 
spotted  stage,  before  attaining  the  adult  coloration. 

The  young  of  spotted  salamanders  are  without 
spots  (genera  Amblystoma  and  Salamandra  e  g.)  ;  so 
that  unspotted  species  resemble  the  young  of  the 
spotted.  In  many  species  of  birds  of  more  or  less  uni- 
form patterns  of  coloration,  the  young  are  spotted.  In 
some  of  these  the  females  remain  spotted  throughout 
adult  life.  In  some  other  species  both  sexes  retain 
the  spotted  coloration  of  the  young.  The  young  of 
most  deer  are  spotted.  In  the  fallow-deer  (Axis)  the 
adults  retain  the  spotted  coloration,  thus  resembling 
the  young  of  most  of  the  species. 


200    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


3.   INEXACT  PARALLELISM  OR  C^ENOGENY. 

When  the  early  or  transitional  stage  of  a  higher 
form  is  exactly  the  same  as  a  permanent  lower  form, 
the  parallelism  is  said  to  be  "exact."  Such  is  the  re- 
lation of  a  Cnemidophorus  gularis  scalar  is  to  a  Cnemido- 
^phorus  gularis  gularis  as  to  color  characters  ;  and  of  an 
Amblystoma  tigrinum  to  a  permanent  breeding  Siredon 
lichenoides  in  characters  of  higher  structural  value. 

When  the  transitional  stage  of  the  higher  only  re- 
sembles the  lower  form  in  some  one  or  more  features, 
but  not  in  all,  the  parallelism  is  said  to  be  "inexact." 
It  is  evident  that  "exact  parallelism  "  can  only  exist 
between  ancestor  and  descendant  in  the  same  re- 
stricted line,  and  can  be  therefore  only  demonstrated 
in  the  case  of  the  nearest  relatives,  between  which  a 
perfect  phylogeny  is  known.  So  soon  as  new  subordi- 
nate characters  are  assumed,  or  a  change  in  the  order 
of  appearance  of  characters  supervenes,  the  parallel- 
ism becomes  "inexact,"  and  such  is  the  kind  of  paral- 
lelism usually  observed.  And  it  is  more  inexact  the 
more  widely  removed  in  relationship  are  the  forms 
compared.  Thus  the  parallelism  between  the  embryo 
man  with  five  branchial  slits,  and  the  adult  shark,  is 
very  inexact ;  but  that  between  a  true  fish  and  a  shark 
is  much  less  inexact.  That  between  a  higher  and  a 
lower  shark  is  still  more  exact,  and  so  on.  Exact  par- 
allelism in  growth  is  called  by  Haeckel  palingenesis 
or  palingeny.  The  growth  which  has,  through  changes 
introduced  subsequent  to  the  origin  of  a  line  of  de- 
scent, become  inexact,  or  "falsified,"  is  termed  by  the 
same  author  caenogenesis  or  caenogeny. 


PARALLELISM.  201 

The  superposition  of  characters  which  constitutes 
evolution,  means  that  more  numerous  characters  are 
possessed  by  the  higher  than  the  lower  types.  This 
involves  a  greater  number  of  changes  during  the  on- 
togenetic  growth  of  each  individual  of  the  higher  type. 
In  other  words,  characters  acquired  during  the  phylo- 
genetic  history  are  continually  assumed  by  the  pro- 
gressive form  at  earlier  and  earlier  periods  of  life. 
This  process  has  been  metaphorically  termed  by  Pro- 
fessor Alpheus  Hyatt  and  myself  "acceleration."  All 
progressive  organic  evolution  is  by  acceleration,  as 
here  described.  Retrogressive  evolution  may  be  ac- 
complished by  a  retardation  in  the  rate  of  growth  of 
the  taxonomic  characters,  so  that  instead  of  adding, 
and  accumulating  them,  those  already  possessed  are 
gradually  dropped  ;  the  adults  repeating  in  a  reversed 
order  the  progressive  series,  and  approaching  more 
and  more  the  primitive  embryonic  stages.  This  pro- 
cess I  have  termed  "retardation."  Retardation  is  not 
however,  always  exact,  even  in  retracing  a  true  phylo- 
genetic  line,  whence  in  such  instances  the  process  may 
not  be  correctly  described  as  retardation.  Professor 
Hyatt  has  applied  to  such  types  the  term  "senile," 
and  gerontic  ;  and  to  the  resulting  condition,  the  term 
"senility."  His  observations  on  this  subject  have  been 
made  on  Mollusca,  and  principally  on  the  Cephalo- 
poda, and  are  of  fundamental  importance  in  this  con- 
nection. 

The  history  of  a  type  which  has  passed  through  a 
full  cycle  of  life,  from  its  earliest  appearance  to  its  ex- 
tinction, is  divided  by  Haeckel  into  three  stages,  viz.: 
those  of  its  rise  ;  full  vigor,  as  displayed  by  predomi- 
nance of  variations  and  numbers ;  and  decadence. 
For  these  stages  he  uses  the  expressions  Anaplasis, 


202    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

Metaplasis,  and  Cataplasis.  For  the  processes  which 
bring  about  the  first  and  last  of  these  conditions,  Pro- 
fessor Hyatt  has  used  the  terms  Anagenesis  and  Cata- 
genesis. Catagenesis  is  equivalent  to  degeneracy  and 
has  played  an  important  part  in  organic  evolution.  I 
had  used  the  term  previously  to  Professor  Hyatt  for 
the  same  process,  but  with  a  wider  application ;  ex- 
tending its  use  to  inorganic  nature  as  well.1  (See 
Chapter  IV.  of  this  book.) 

Embryology  has,  however,  revealed  another  series 
of  phenomena  which  in  many  instances  obscure  the 
simplicity  of  the  problem  of  ontogeny  as  presented  in 
the  preceding  pages.  It  was  the  merit  of  Haeckel  to 
generalize  from  the  facts  brought  to  light  by  this  sci- 
ence, so  as  to  present  the  relations  which  subsist  be- 
tween the  primitive  stages  of  all  multicellular  animals. 
This  is  known  as  the  Gastraea  theory.  He  showed 
that  the  primitive  gastric  cavity  of  all  such  animals  is 
produced  by  an  invagination  of  a  portion  of  the  sur- 
face of  a  primitive  sphere  or  morula,  which  results 
from  the  segmentation  of  the  oosperm.  This  hollow 
half-sphere  he  termed  the  gastrula,  and  the  theoretical 
primitive  animal  which  corresponds  to  it  he  called  the 
Gastraea.  Marine  animals  very  similar  to  this  Gas- 
traea have  been  discovered.  Haeckel  showed,  how- 
ever, that  gastrulas  are  not  all  alike,  since  they  differ 
in  the  extent  to  which  the  segmentation  of  the  oosperm 
may  be  carried,  and  the  rate  of  segmentation  of  differ- 
ent parts  of  it.  Thus  early  do  inexact  parallelisms 
arise.  From  this  point  onwards  special  peculiarities 
of  the  various  developmental  lines  appear,  some  of 
which  have  especial  reference  to  the  necessities  of  em- 
bryonic life.  Hence  the  trochosphere  stage  of  so  many 

\Origin  of  the  Fittest ,  p.  422. 


PARALLELISM.  203 

invertebrate  forms,  and  the  nauplius  and  zoaea  of  the 
Crustacea. 

Such  are  the  statoblasts  which  are  resting-stages 
for  the  embryos  of  fresh-water  sponges  and  Polyzoa, 
and  the  glochidia  of  the  Unionidae,  which  are  wanting 
in  the  marine  forms  of  the  same  orders.  Such  are  the 
amnion  and  allantois  of  certain  Vertebrata  and  the 
placenta  of  certain  Mammalia,  which  have  no  refer- 
ence to  any  structures  but  their  own  residua,  found  in 
the  adults  of  those  animals. 

A  remarkable  instance  of  this  state  of  things  ap- 
pears in  the  history  of  the  evolution  of  the  insects.  It 
is  quite  impossible  to  understand  this  history  without 
believing  that  the  larval  and  pupal  states  of  the  high- 
est insects  are  the  results  of  a  process  of  degeneracy 
which  has  affected  the  middle  periods  of  growth,  but 
not  the  mature  results.  The  earliest  insects  are  the 
Orthoptera,  which  have  active  aggressive  larvae  and 
pupae,  undergoing  the  least  changes  in  their  meta- 
morphosis (Ametabola),  and  never  getting  beyond  the 
primitive  mandibulate  condition  at  the  end.  The  meta- 
morphosis of  the  jawed  Neuroptera  is  little  more 
marked,  and  they  are  one  of  the  oldest  orders. 

The  highest  orders  with  jaws  undergo  a  marked 
metamorphosis  (Coleoptera,  Hymenoptera),  the  Hy- 
menoptera  even  requiring  artificial  intervention  in 
some  instances  to  make  it  successful.  Finally,  the 
most  specialized  orders,  the  suctorial  Diptera  and 
Lepidoptera,  especially  the  latter,  present  us  with  very 
unprotected  more  or  less  parasitic  larval  stages,  both 
active  and  inactive.  These  animals  have  evidently  de- 
generated, but  not  so  as  to  prevent  their  completing  a 
metamorphosis  necessary  for  purposes  of  reproduction. 
As  is  well  known,  many  imagines  (Saturniidae,  CEstridae) 


204    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

can  perform  no  other  function,  and  soon  die,  while  in 
some  Diptera  the  incomplete  larvae  themselves  repro- 
duce, so  that  the  metamorphosis  is  never  completed. 

This  history  is  parallel  to  that  proposed  by  Dohrn 
to  account  for  the  origin  of  the  Ammocoetes  larval 
stage  of  the  Marsipobranchii.  He  supposes  this  form 
to  be  more  degenerate  than  the  corresponding  stage  of 
its  probable  ancestral  type  in  the  ancestral  line  of  the 
Vertebrata.  An  inactive  life  in  mud  is  supposed  by 
Dohrn  to  have  been  the  effective  cause.  An  inactive 
life  on  the  leaves  of  plants,  or  in  dead  carcases,  has 
probably  been  the  cause  of  the  same  phenomenon  in 
the  Lepidoptera  and  Diptera. 

Thus  we  have  developed  an  ontogeny  within  an 
ontogeny,  and  a  phylogeny  within  a  phylogeny.  These 
facts  do  not,  however,  affect  the  general  result  in  the 
least.  They  only  show  us  that  the  persistent  larvae 
of  those  animals  which  possess  them,  have  a  history  of 
their  own,  subject  to  the  same  laws  of  evolution  as 
the  adults.  It  results  that  in  many  cases  the  phy- 
logeny can  only  be  determined  by  the  discovery  and 
investigation  of  the  ancestors  themselves,  as  they  are 
preserved  in  the  crust  of  the  earth.  In  all  cases  this 
discovery  confirms  and  establishes  such  definite  con- 
clusions as  may  be  derived  from  embryology.  It  is 
also  clear  that  on  the  discovery  of  phylogenetic  series 
it  becomes  at  once  possible  to  determine  the  nature  of 
defective  types.  It  becomes  possible  to  ascertain 
whether  their  rudimental  parts  represent  the  begin- 
nings of  organs,  or  whether  they  are  the  result  of  a 
process  of  degeneration  of  organs  once  well  devel- 
oped. 

An  excellent  illustration  of  inexact  parallelism  is 
to  be  found  on  comparison  of  man  with  the  lower  Ver- 


PARALLELISM.  205 

tebrata.  I  have  pointed  out1  that  in  the  structure  of 
his  extremities  and  dentition,  he  agrees  with  the  type 
of  Mammalia  prevalent  during  the  Eocene  period 
(cfr.  Phenacodus).  Hence  in  these  respects  he  re- 
sembles the  immature  stages  of  those  mammals  which 
have  undergone  special  modifications  of  limbs  and  ex- 
tremities, such  as  Ungulata  in  which  caenogeny  has 
not  obliterated  the  early  stages  from  the  embryonic 
record.  These  forms  are  probably  extinct.  I  have 
also  shown2  that  in  the  shape  of  his  head  man  resem- 
bles the  embryos  of  all  Vertebrata,  in  the  protuberant 
forehead,  and  vertical  face  and  jaws.  In  this  part  of 
the  structure  most  Vertebrata  have  grown  farther  from 
the  embryonic  type  than  has  man,  so  that  the  human 
face  may  be  truly  said  to  be  the  result  of  a  process  of 
retardation.  Nevertheless,  in  the  structure  of  his  ner- 
vous, circulatory,  and  for  the  most  part,  of  his  repro- 
ductive system,  man  stands  at  the  summit  of  the  Ver- 
tebrata. It  is  in  those  parts  of  his  structure  that  are 
necessary  to  supremacy  by  force  of  body  only,  that 
man  is  retarded  and  embryonic. 

5.  OBJECTIONS  TO  THE  DOCTRINE  OF  PARAL- 
LELISM. 

An  objection  to  the  theory  of  parallelism  in  its  full 
sense  has  been  recently  put  forward  by  Mr.  C.  Her- 
bert Hurst.3  He  says,  "My  object  now  is  to  show 
that  in  neither  case  can  a  record  of  the  variation  at 
any  one  stage  of  evolution  be  preserved  in  the  ontog- 
eny, much  less  can  the  ontogeny  come  to  be  a  series  of 

1 "  The  Relation  of  Man  to  the  Tertiary  Mammalia,"  Penn  Monthly,  1875; 
Origin  of  the  Fittest,  268. 

2  "  The  Developmental  Significance  of  Human  Physiognomy,"  American 
Naturalist,  June,  1883  ;  Origin  of  the  Fittest,  1887,  p.  281. 

ZXatural  Science,  1893,  p.  195. 


206    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

stages  representing  in  proper  chronological  order  some 
of  the  stages  of  adult  structure  which  have  been  passed 
through  in  the  course  of  evolution."  Again:  "The 
early  stages  of  the  fish  embryo  are  very  like  those  of 
the  bird  embryo.  These  two  do  correspond  to  each 
other.  The  statement  that  the  embryonic  structure 
of  a  bird  follows  a  course  which  is  from  beginning  to 
end  roughly  parallel  with,  but  somewhat  divergent 
from,  the  course  followed  by  a  fish,  is  borne  out  by 
the  actual  facts.  A  bird  does  not  develop  into  a  fish 
and  then  into  a  reptile,  and  then  into  a  bird.  There  is 
no  fish-stage,  no  reptile-stage,  in  its  ontogeny.  The 
adult  resembles  an  adult  fish  only  very  remotely.  Every 
earlier  stage  resembles  the  corresponding  earlier  stage 
of  the  fish  more  closely.  There  is  a  parallelism  be- 
tween the  two  ontogenies.  There  is  no  parallelism  be- 
tween the  ontogeny  and  the  phylogeny  of  either  a  bird  or 
any  other  animal  whatever.  A  seeming  parallelism  will 
fall  through  when  closely  examined."  "  The  promise 
that  this  theory  gave  of  serving  as  the  guide  to  knowl- 
edge of  past  history  without  the  labor  involved  in  pale- 
ontological  research,  was  indeed  tempting  :  and  where 
the  royal  road  to  learning  has  been  shown  by  it,  it  is  not 
surprising  that  some  zoologists  should  have  entered 
for  the  race  along  this  road.  To  what  goal  that  road 
has  led  may  be  learned  by  a  comparison  of  the  nu- 
merous theories  as  to  the  ancestry  of  the  <  Chordata ' 
which  have  been  put  forward  by  those  who  have 
adopted  the  theory  without  enquiring  as  to  its  valid- 
ity." 

I  have  made  this  quotation  as  showing  the  point  of 
view  from  which  the  doctrine  of  parallelism  when  in- 
correctly stated  may  be  assailed.  There  is  truth  in 
the  author's  accusation  that  embryologists  who  have 


PARALLELISM.  207 

not  used  their  results  with  proper  caution,  have  been 
frequently  led  to  incorrect  and  even  absurd  results. 
The  errors  of  this  class  of  biologists  are  mainly  due  to 
their  ignorance  of  species  in  the  adult  state,  and  their 
ignorance  of  systematic  biology  or  taxonomy.  They 
profess  to  regard  this  branch  of  the  science  as  only 
suitable  for  beginners,  and  as  comparatively  unim- 
portant, as  compared  with  their  own  ;  yet  one  might 
as  well  attempt  the  study  of  philology  without  a  knowl- 
edge of  alphabets,  as  to  study  phylogeny  without  the 
knowledge  of  natural  taxonomy.  The  correct  discrim- 
ination of  species,  genera,  etc.,  imposes  much  greater 
burdens  on  the  faculty  of  judgment,  than  does  any- 
thing to  be  found  in  any  science  which  includes  obser- 
vation and  record  only.  But  Mr.  Hurst's  statement  is 
somewhat  overdrawn,  and  he  does  not  give  embryolo- 
gists  the  credit  which  is  due  to  their  theory  of  recapitu- 
lation. I  think  he  will  find  the  following,  which  I  wrote 
in  I8721  to  be  a  correct  statement  of  the  facts,  and  a 
fair  induction  as  to  principles. 

"The  smaller  the  number  of  structural  characters 
which  separate  two  species  when  adult,  the  more 
nearly  will  the  less  complete  of  the  series  be  identical 
with  an  incomplete  stage  of  the  higher  species.  As 
we  compare  species  which  are  more  and  more  differ- 
ent, the  more  necessarily  must  we  confine  the  asser- 
tion of  parallelism  to  single  parts  of  the  animals,  and 
less  to  the  whole  animal.  When  we  reach  species  as 
far  removed  as  man  and  a  shark,  which  are  separated 
by  the  extent  of  the  series  of  vertebrated  animals,  we 
can  only  say  that  the  infant  man  is  identical  in  its  nu- 
merous origins  of  the  arteries  from  the  heart,  and  in 

the  cartilaginous    skeletal   tissue,    with   the    class    of 
/ 

IPenn  Monthly,  1872.     Origin  of  the  Fittest,  1887,  p.  8. 


208    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

sharks,  and  in  but  few  other  respects.  But  the  im- 
portance of  this  consideration  must  be  seen  from  the 
fact  that  it  is  on  single  characters  of  this  kind  that  the 
divisions  of  the  zoologist  depend.  Hence  we  can  say 
truly  that  one  order  is  identical  with  an  incomplete 
stage  of  another  order,  though  the  species  of  the  one 
may  never  at  the  present  time  bear  the  same  relation 
in  their  entirety  to  the  species  of  the  other.  Still  more 
frequently  can  we  say  that  such  a  genus  is  the  same  in 
character  as  a  stage  passed  by  the  next  higher  genus ; 
but  when  we  can  say  this  of  species,  it  is  because  their 
distinction  is  almost  gone.  It  will  then  depend  on  the 
opinion  of  the  naturalist  as  to  whether  the  repressed 
characters  are  permanent  or  not.  Parallelism  is  then 
reduced  to  this  definition  :  that  each  separate  charac- 
ter of  every  kind,  which  we  find  in  a  species,  repre- 
sents a  more  or  less  complete  stage  of  the  fullest 
growth  of  which  the  character  appears  to  be  capable. 
In  proportion  as  those  characters  in  one  species  are 
contrasted  with  those  of  another  by  reason  of  their 
number,  by  so  much  must  we  confine  our  comparison 
to  the  characters  alone,  and  the  divisions  they  repre- 
sent; but  when  the  contrast  is  reduced  by  reason  of 
the  fewness  of  differing  characters,  so  much  the  more 
truly  can  we  say  that  the  one  species  is  really  a  sup- 
pressed or  incomplete  form  of  the  other  The  denial 
of  this  principle  by  the  authorities  cited  has  been  in 
consequence  of  this  relation  having  been  assigned  to 
orders  and  classes,  when  the  statement  should  have 
been  confined  to  single  characters,  and  divisions  char- 
acterized by  them.  There  seems,  however,  to  have 
been  a  want  of  exercise  of  the  classifying  quality  or 
power  of  '  abstraction  '  of  the  mind  on  the  part  of  the 
objectors." 


PARALLELISM.  209 

It  is  nevertheless  true  that  the  records  brought  to 
light  by  embryologists  are  very  imperfect,  and  have  to 
be  carefully  interpreted  in  order  to  furnish  reliable  evi- 
dence as  to  the  phylogeny  of  the  species  examined. 
An  illustration  of  this  is  the  fact  that  the  species  char- 
acters appear  in  many  embryos  before  those  which  de- 
fine the  order  or  the  family,  although  it  is  certain  that 
the  latter  appeared  first  in  the  order  of  time.  Most  of 
the  important  conclusions  as  to  the  phylogeny  of  Ver- 
tebrata  demonstrated  by  paleontology  have  never  been 
observed  by  embryologists  in  the  records  of  the  spe- 
cies studied  by  them.  Thus  I  have  shown  that  it  is 
certain  that  in  the  amniote  vertebrates  the  intercen- 
trum  of  the  vertebral  column  has  been  replaced  by  the 
centrum  ;  yet  no  evidence  of  this  fact  has  been  ob- 
served by  an  embryologist.  If  we  could  study  the  em- 
bryonic development  of  the  vertebral  column  of  the 
Permian  and  Triassic  Reptilia,  the  transition  would  be 
observed,  but  in  recent  forms  caenogeny  has  progressed 
so  far  that  no  trace  of  the  stage  where  the  intercentrum 
existed  can  be  found. 

Again  I  have  demonstrated  by  paleontological  evi- 
dence that  the  lines*  of  the  ungulate  Mammalia  origi- 
nated from  a  bunodont  pentadactyle  plantigrade  an- 
cestor ;  but  embryonic  research  has  failed  to  discover 
the  preservation  of  a  record  of  this  fact  in  the  ungu- 
lates at  present  existing.  The  embryo  of  the  horse  is 
not  pentadactyle,  nor  even  tridactyle,  although  tri- 
dactyle  horses  persisted  late  in  geologic  time.  Nor 
has  embryonic  research  demonstrated  a  four-toed 
stage  in  the  Bovidae  (oxen,  etc.),  although  there  is  no 
doubt  that  they  descended  directly  from  an  ancestor 
so  characterized.  Any  number  of  similar  cases  might 
be  cited  to  show  the  prevalence  of  inexact  parallelism 


210    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

or  caenogeny.  If  we  could  study  the  embryology  of 
the  many  extinct  forms  of  life,  the  missing  stages 
would  all  be  found,  but  as  we  have  not  the  opportun- 
ity of  pursuing  this  important  research,  we  have  to 
rely  on  paleontology  for  our  phylogeny.  Paleontology 
is  and  always  will  be  imperfect,  but  all  that  we  get  is 
palingeny,  or  the  phylogeny  itself,  and  not  an  inverted 
and  distorted  record  of  it. 


CHAPTER  IV.— CATAGENESIS. 


WE  HAVE  been  principally  occupied  so  far  with 
progressive  evolution  or  anagenesis.  Reference 
has,  however,  been  made  to  retrogressive  .evolution  or 
degeneracy,  in  Chapter  III.,  in  describing  the  evolution 
of  the  Vertebrata,  and  will  be  in  Chapter  V.,  under  the 
caption  "Disuse  in  Mammalia."  Degeneracy  has,  how- 
ever, played  a  more  important  part  in  creation  than 
would  be  suspected  from  these  references,  and  I  pro- 
pose in  the  present  chapter  to  go  more  fully  into  its 
phenomena,  which,  in  the  broadest  sense,  I  have  called 
collectively  Catagenesis. 

As  evidence  for  degeneracy  as  a  factor  in  evolution 
we  naturally  appeal  first  to  examples  in  the  life  histo- 
ries of  plants  and  animals  which  are  known  to  us;  and 
then  examine  the  records  of  the  past,  in  the  light  thus 
gained,  for  evidence  of  degeneracy  in  vegetable  and 
animal  phylogeny.  In  both  directions  we  are  met  by 
an  embarras  de  richesse,  and  a  few  conspicuous  cases 
will  have  to  suffice. 

The  parasitic  copepod  Crustacea  undergo  a  retro- 
grade metamorphosis,  which  commences  at  different 
periods  of  the  growth  history  of  different  genera.  Says 
Claus  :  "Many  parasitic  Copepoda,  however,  pass 


212    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

over  the  series  of  nauplius  forms  [which  are  traversed 
by  other  copepods]  and  the  larva,  as  soon  as  hatched, 
undergoes  a  moult,  and  appears  at  once  in  the  youngest 

Cyclops  form  with 
antennae  adapted 
for  adhering,  and 
mouth  -parts  for 
piercing.  From  this 
stage  they  under- 
go a  retrogressive 
metamorphosis,  in 
which  they  become 
attached  to  a  host, 
lose  more  or  less 
completely  the  seg- 
mentation of  the 
body,  which  grows 
irregular  in  shape, 
cast  off  their  swim- 
ming feet,  and  even 
lose  the  eye,  which 
was  originally  pres- 
ent  (Lerndapodd). 
The  males,  how- 
ever, in  such  cases 
often  remain  small 

Fig.  v.-Lerna>abranchialis;a,  male  ;  *,  non-     and     dwarfed,      and 


degenerate  female;  c,  female  after  fertilization     adhere 

undergoing  metamorphosis  ;  d,  do.  with  egg  sacs,  , 

natural  size.    From  Claus.  more        than        One, 

firmly  to  the  body 

of  the  female  in  the  region  of  the  genital  opening.  In 
the  Lerncea  such  pigmy  males  were  for  a  long  time 
vainly  sought  for  upon  the  very  peculiarly  shaped  body 
of  the  large  female  (Fig.  52),  which  carries  egg-tubes. 


CA  TA  GENESIS.  2 1 3 

At  last  it  was  discovered  that  the  small  Cyclops -like 
males  lead  an  independent  life  and  swim  about  freely 
by  means  of  their  four  pairs  of  swimming  feet,  and 
that  the  females  in  their  copulatory  stage  resemble  the 
males,  and  that  it  is  only  after  copulation  that  they 
(the  females)  become  parasitic  and  undergo  the  con- 
siderable increase  in  size  and  modification  of  form 
which  characterizes  the  female  with  egg-tubes." 

A  degeneracy  of  the  females  of  a  remarkable  char- 
acter occurs  in  the  insects  of  the  order  Strepsiptera. 
Here  the  female  during  the  larval  stage,  bores  its  way 
into  the  body  of  a  hymenopterous  insect  and  soon  un- 
dergoes a  moult.  At  this  time  they  shed  their  three 
pairs  of  well-developed  legs,  and  become  a  parasitic 
maggot,  which  lives  on  the  body  of  the  host.  The 
males  do  not  undergo  this  degeneracy  but  retain  the 
six  legs  and  two  pairs  of  wings  common  to  the  class 
Insecta. 

A  notorious  example  of  degeneracy  among  the  Mol- 
lusca  is  offered  by  the  Entoconcha  mirabilis.  Says  J. 
S.  Kingsley  :  "  So  greatly  has  parasitism  altered  the 
form  of  the  body,  and  all  of  the  organs,  that  the  proper 
position  of  this  form  among  the  gastropods  is  far  from 
certain,  some  placing  it  near  Natica.  Indeed,  were  it 
not  for  the  characters  afforded  by  the  young,  its  posi- 
tion among  the  Mollusca  would  not  be  suspected. 
Some  thirty  years  ago  [before  1885]  Johannes  Miiller 
found  in  some  specimens  of  Synapta  digitata  an  inter- 
nal worm-like  parasite,  attached  by  one  extremity  to 
the  alimentary  canal,  while  the  other  end  hung  free 
in  the  perivisceral  cavity."  "  In  one  specimen  of  Syn- 
apta out  of  one  or  two  hundred  this  strange  form  oc- 
curs. It  is  a  sac,  the  upper  part  bearing  the  female, 
and  the  lower  the  male  reproductive  organs,  while  the 


214    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


centre  of  the  body  serves  for  a  while  as  a  broodpouch, 
the  embryos  later  passing  out  from  an  opening  at  the 

free  end  of  the  body 
of  the  parent.  The 
eggs  undergo  a  toler- 
ably regular  develop- 
ment, producing  a 
velum,  shell,  andoper- 
culum,  the  later  stages 
being  found  free  in  the 
body  -cavity  of  the 
host." 

The  preceding  ex- 
amples illustrate  the 
degenerating  or  cata- 
genetic  effect  of  a 
parasitic  life.  We  will 
now  observe  the  cor- 
responding effect  of  a 
sedentary  life,  which 
may  be  called  earth- 
parasitism.  As  an  ex- 
ample of  this  I  select 
the  well-known  case 
of  the  lowest  of  the 
Vertebrata,  the  Tuni- 
cata 

Fig-  53-  —  A  Synapta  digitata  with  para- 

sitic Entoconcha  ;  B,  a  portion  of  Synapta,  The  embryo  ascid- 

with  Entoconcha  (F)  enlarged  ;    a,  point  of     •  i  .1         r  r 

attachment  ;  b,  blood  vessels  ;  /,  female  por- 

tion  ;  *',  intestine;  m,  male  portion  ;  me,  me-     a     tadpole-like      larva 
sentery.     From  Kingsley. 


actiyely 

through  the  sea  by  vibrating  its  long  tail.  After  a 
short  free-swimming  existence  the  fully  developed, 
tailed  larva  fixes  itself  by  its  anterior  adhering  papillae 


CA  TA  GENESIS.  2 1 5 

to  some  foreign  object,  and  then  undergoes  a  remark- 
able series  of  retrogressive  changes,  which  convert  it 
into  the  adult  ascidian.  The  tail  atrophies,  until  noth- 
ing is  left  but  some  fatty  cells  in  the  posterior  part  of 
the  trunk.  The  adhering  papillae  disappear  and  are 
replaced  functionally  by  a  growth  of  the  test  over  neigh- 
boring objects.  The  nervous  system  with  its  sense- 
organs  atrophies,  until  it  is  reduced  to  the  single  small 
ganglion  placed  on  the  dorsal  edge  of  the  pharynx, 
and  a  slight  nerve-cord  running  for  a  short  distance 
posteriorly.  Slight  changes  in  the  shape  of  the  body 
and  a  further  growth  and  differentiation  of  the  branchial 
sac,  peribranchial  cavity,  and  other  organs  now  pro- 
duce gradually  the  structure  found  in  the  adult  ascid- 
ian (Herdman).  It  is,  however,  to  be  noted  that  in 
the  order  Larvacea,  this  retrograde  metamorphosis 
does  not  take  place.  It  embraces  the  single  family 
Appendiculariidae,  which  includes  Tunicata  which  pre- 
serve the  tail,  notochord,  and  other  larval  features,  and 
lead  a  free-swimming  existence  in  the  ocean. 

On  the  Tunicata,  Herdman  makes  the  following 
general  observations.  "  (i)  In  the  ascidian  embryo 
all  the  more  important  organs  (e.  g.  notochord,  neural 
canal,  archenteron)  are  formed  in  essentially  the  same 
manner  as  they  are  in  amphioxus  and  other  Chordata. 
(2)  The  free-swimming  tailed  larva  possesses  the  es- 
sential characters  of  the  Chordata,  inasmuch  as  it  has 
a  longitudinal  skeletal  axis  (the  notochord),  separat- 
ing a  dorsally  placed  nervous  system  (the  neural  canal) 
from  a  ventral  alimentary  canal  (archenteron)  ;  and 
therefore  during  this  period  of  its  life  history  the  ani- 
mal belongs  to  the  Chordata.  (2)  The  Chordata  larva 
is  more  highly  organized  than  the  adult  ascidian,  and 
therefore  the  changes  by  which  the  latter  is  produced 


DlPLOGLOSSA 

LEPTO 

Pygopodidae 

Zonuridae 

Anguidae 

Teidse 

Gerrhosauridae 

I.  Limbs,  two  pair 
a.   Digits  5-4 

Tejus 

b.  Digits  4-5 

Tretioscineus 
Micrablepharus 
Gymopthalmus 

c.  Digits  4-4 

Sauresia 

Scolecosaurus 

Saurophis 

d.  .Digits  4-3 

• 

e.  Digits  3-4 

/.  Digits  3-3 

Microdactylus 

g.  Digits  3-2 

Herpetochalcis 

h.  Digits  2-4 

/'.  Digits  2-3 

>.  Digits  2  2 

£.  One  or  both 
monodactyle 

Chamaesaura 

Panolopus 

Cophias 
Ophiognomon 

Caetia 

II.  Fore  limbs  only 

Propus  (digits  o> 

III.  Hind  limbs  only 

Pygopus 
Cryptodelma 
Delma 
Pletholax 
Aprasia 
Lialis 

Mancus 

Pseudopus 
Opheodes 
Hyalosaurus 

IV.  No  limbs 

Opheosaurus 
Dopasia 
Anguis 

GLOSSA 

ANNIEL- 

LOIDEA 

ANNULATI 

Scincidae 

Acontiidae 

Dibamidae 

Anelytropsidae 

Anniellidae 

Hagria 

Heteropus 
Ristella 
Menetia 

Gongyloseps 
Chiamela 
Rhinoseineus 
Tetradactylus 
Miculia 
Chalcidoseps 
Blepharactisis 
Sphenops 

Zygnopsis 

Allodactylus 

Tridentulus 
Chalcides 
Hemiergis 
Siaphus 
Phaneropis 
Sepomorphus 
Sphenoscineus 
Sepsina 

Nessia 

Hemipodium 

Anisoterma 

Lerista 
Eumecia 
Heteromeles 

Dimeropus 
Chelomeles 

Brachystopus 
Oncopus 
Brachymeles 
Anomalopus 
Coloscincus 
Furcillus 
Dicloniscus 

Evesia 

EuchirotK.ae  (di- 
gits 3-5) 

Ollochirus 
Dumerlia 
Scelotes 
Soridia 
Podoclonium 

Dibamus 

Opheoscincus 
Herpetosaura 
Sepophis 
Herpetoseps 
Opheomorus 

Acontias 
Typhlacontias 

Anelytropsis 
Feylinia 
Typhlosaurus 

Anniella 

Amphisba:na 
Rhineura 
Lepidosternum 
Trogonophidae 

218    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

from  the  former  may  be  regarded  as  a  process  of  de- 
generation. The  important  conclusion  drawn  from  all 
this  is,  that  the  Tunicata  are  the  degenerate  descend- 
ants of  a  group  of  the  primitive  Chordata  "  (=Verte- 
brata). 

The  degeneracy  of  the  Tunicata  follows  imme- 
diately their  assumption  of  the  sessile  condition.  Some 
of  the  degenerate  forms  which  are  not  sessile,  are  sup- 
posed to  be  the  free  descendants  of  sessile  forms. 

Among  the  craniate  Vertebrata,  most  conspicuous 
examples  of  degeneracy  are  to  be  seen  in  the  reduction 
and  loss  of  limbs  in  certain  Batrachia  and  in  many 
Reptilia.  In  both  classes  successive  loss  of  phalanges 
and  digits  form  series  in  several  groups  of  salamanders 
and  lizards,  and  in  both  these  orders  there  are  forms 
with  the  limbs  rudimental  or  altogether  wanting.  In 
Batrachia,  the  genus  Amphiuma  displays  rudimental 
limbs  with  minute  digits  numbering  two  or  three  on 
each  limb.  In  the  Caeciliidae,  the  limbs  are  wanting. 
Both  types  are  subterranean  in  their  habits.  I  give  the 
annexed  table  of  the  Lacertilia  with  degenerate  limbs, 
which  it  will  be  observed  are  found  in  eleven  distinct 
families.  (Pp.  216-217.) 

Finally,  in  the  snakes  (Ophidia)  the  limbs  have 
totally  disappeared,  rudiments  only  remaining  in  the 
boas  and  pythons  and  their  allies. 

Paleontology  renders  it  clear  that  this  reduction  is 
a  case  of  degeneracy,  since  both  the  Ophidia  and  La- 
certilia can  be  traced  to  Reptilia  of  the  Permian  epoch, 
which  have  well-developed  limbs.  This  degeneracy  is 
allied  to  subterranean  or  terrestrial  habits.  It  is  prob- 
able that  the  primitive  snakes  sought  concealment  in 
cavities  of  the  earth  and  beneath  rocks  and  logs,  and 
spent  much  of  their  time  in  narrow  quarters,  where 


CA  TA  GENESIS.  2 19 

limbs  would  be  of  no  use  to  them.  Some  of  them,  the 
Angiostomata,  are  now  subterranean  in  their  habits, 
and  most  of  them  are  blind,  or  nearly  so.  These  forms 
present  rudiments  of  limbs,  which  leads  to  the  supposi- 
tion that  they  are  near  to  the  ancestral  types.  From 
such  forms  they  developed  a  type  which  has  proved 
competent  to  compete  successfully  with  other  verte- 
brates on  the  ground,  in  the  water,  and  in  the  trees  of 
the  forest. 

From  what  has  gone  before  it  is  now  clear  that 
while  kinetogenesis  is  a  factor  in  progressive  evolu- 
tion, the  reverse  process,  or  akinetogenesis,  is  as  defi- 
nite a  factor  in  degeneracy.  The  evidence  derived 
from  parasitism  and  sedentary  modes  of  life  is  conclu- 
sive in  this  direction. 

I  now  cite  another  example  of  catagenesis  which 
throws  much  light  on  the  origin  of  the  vegetable  king- 
dom. I  have  advanced  the  hypothesis1  that  plants 
are  the  degenerate  descendants  of  protozoan  animal 
ancestors,  and  I  will  now  produce  some  of  the  evi- 
dence on  which  the  hypothesis  rests.  The  Myxomy- 
cetes  or  Mycetozoa  occupy  debatable  ground  between 
the  vegetable  and  animal  kingdoms.  They  seem  at 
one  period  of  their  history  to  pertain  to  the  former  and 
at  another  to  the  latter. 

These  organic  beings  are  claimed  by  both  botanists 
and  zoologists,  the  former  placing  them  with  the 
Fungi,  the  latter  including  them  in  the  Protozoa. 
The  fact  is  that  in  their  mature  form  they  enter  the 
Fungi,  while  in  their  early  stages  they  are  Protozoa. 
They  have  distinct  reproductive  structures,  which  pro- 
duce spores.  From  each  spore  issues  a  "flagellula," 
which  is  a  simple  cell  with  a  flagellum,  not  apparently 

1  Origin  of  the  Fittest,  pp.  431-432. 


220    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

different  from  a  monad.  The  flagellum  is  early  lost, 
and  the  cell  is  then  termed  an  amcebula,  since  it  does 
not  differ  materially  from  an  amoeba.  Its  movements 
are  similar,  and  it  puts  forth  short  pseudopodia.  When 
these  amcebulae  come  in  contact  with  each  other  they 


Fig.  54. — Mycetozoa  (from  Lankester  after  Du  Bary).  1-6,  Germination 
of  spore  (i)  of  Tricheavaria,  showing  the  emerging  flagellula ;  (4-5)  and  its 
conversion  into  an  amcebula  (6).  7-18,  Series  leading  from  spore  to  plasmo- 
dium  phase  of  Chondrioderma.  dijfforma  ;  7,  spore ;  10,  flagellula  ;  12,  amoe- 
bula  ;  14,  apposition  of  two  amcebulae ;  15-17,  fusions;  18,  plasmodium.  19- 
20,  Spore-fruit  (cyst)  of  Physarum  leucoph&um  X  25  ;  the  former  from  the  sur- 
face, the  latter  in  section  with  the  spores  removed  to  show  the  sustentacular 
network  or  capillitium.  21,  Section  of  the  spore-cyst  of  Dydymium  squamulo- 
sum,  with  the  spores  removed  to  show  the  radiating  capillitium  x,  and  the 
stalk. 

fuse,  often  in  large  numbers,  forming  a  continuous 
gelatinous  sheet,  the  plasmodium  (Fig.  54),  which 
may  have  several  square  inches,  and  even  feet  of  sur- 
face. At  the  proper  time  reproductive  organs  form 
on  this  surface  in  the  form  of  capsules  (sporangia), 
which  may  or  may  not  be  supported  on  peduncles,  and 


CA  TA  G£N£SfS.  22 1 

which  are  filled  with  minute  cyst-like  masses  of  proto- 
plasm, or  spores.  As  already  stated,  these  spores 
give  issue  to  flagellula. 

We  have  in  the  life  of  the  Mycetozoa,  if  not  the 
actual  origin  of  the  vegetable  from  the  animal  king- 
dom, a  case  closely  similar  to  it  in  a  collateral  phylum. 
The  process  is  one  of  degeneracy  through  the  assump 
tion  of  a  sessile  life,  or  earth-parasitism ;  an  example  of 
akinetogenesis.  The  paleontology  of  animals  has  ab- 
solutely established  the  fact  that  the  predecessors  of 
all  characteristic  or  specialized  types  have  been  un- 
specialized  or  generalized  types,  "neither  one  thing 
nor  another."  It  may  then  be  regarded  as  almost  cer- 
tain that  the  ancestors  of  the  present  higher  types  of 
plants  were  more  animal-like  than  they;  that  the  forms 
displaying  automatic  movements  were  more  numerous, 
and  the  difficulty  of  deciding  on  the  vegetable  or  ani- 
mal nature  of  a  living  organism  greater  than  it  is  now. 
Hence  it  may  be  concluded  that  "animal"  bathmism 
has  from  time  to  time  undergone  retrograde  meta- 
morphosis producing  as  a  result  the  permanent  form 
of  life  which  we  call  vegetable.  Given  spontaneous 
movement  (i.  e.  growth)  and  surrounding  conditions, 
and  the  resultant  product  must  be  structures  adapted 
to  their  surroundings,  just  as  the  plastic  clay  is  fitted 
to  its  mould.  And  this  is  essentially  the  distinguishing 
character  of  vegetable  teleology  as  compared  with  ani- 
mal. In  the  average  plant  we  see  adaptation  to  con- 
ditions permitted  by  unconscious  nutrition  and  repro- 
duction ;  in  the  animal,  adaptation  to  a  greater  variety 
of  conditions,  due  to  the  presence  of  sensation  or  con- 
sciousness. 

In  closing   Part   I.  of  this  book,  I  desire  to  point 
out  the  conclusion  which  has,  I   think,  been  reached. 


222    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

It  has  been  proved,  as  it  appears  to  me,  that  the  vari- 
ation which  has  resulted  in  evolution  has  not  been 
multifarious  or  promiscuous,  but  in  definite  directions. 
It  has  been  shown  that  phylogeny  exhibits  a  progres- 
sive advance  along  certain  main  lines,  instead  of  hav- 
ing been  indefinite  and  multifarious  in  direction. 

It  is  not  denied  that  many  lines  of  variation  have 
been  at  one  geologic  period  and  another  discontinued. 
It  is  also  true  that  certain  divergences  from  the  main 
lines  have  appeared,  and  that  minor  and  secondary 
variations  have  occurred.  Such  variations  do  not  seem 
to  have  had  any  material  effect  on  the  general  course 
of  evolution.  In  many  cases  such  variations  from 
main  lines  might  be  compared  to  the  undulations  in 
the  course  of  a  stream,  which  nevertheless  seeks  its 
lowest  level  in  spite  of  all  temporary  obstacles.  Pro- 
fessor Scott  has  termed  these  temporary  variations  "nu- 
tations," in  an  able  article  on  the  subject.1  "Sports" 
seem  to  have  been  of  no  importance  in  evolution  what- 
ever. 

I  American  Journal  Set.  Arts,  Vol.  XLVIII.,  1894,  p.  355. 


PART  II. 


THE  CAUSES  OF  VARIATION, 


PRELIMINARY. 


IN  Part  II.,  which  treats  of  the  causes  of  variations, 
I  propose  to  cite  examples  of  the  direct  modifying 
effect  of  external  influences  on  the  characters  of  indi- 
vidual animals  and  plants.  These  influences  fall  nat- 
urally into  two  classes,  viz.,  the  physico-chemical 
(molecular),  and  the  mechanical  (molar).  The  modi- 
fications so  presented  are  supposed  to  be  the  result  of 
the  action  of  the  causes  in  question,  continued  through- 
out geologic  time.  To  the  two  types  of  influence 
which  thus  express  themselves  in  evolution,  I  have 
given  the  names  Physiogenesis1  and  Kinetogenesis. 
The  inheritance  of  character  is  assumed  in  this  sec- 
tion, and  the  reason  for  so  doing  will  be  considered 
later,  in  the  third  section  of  this  book. 

In  the  animal  kingdom  we  may  reasonably  suppose 
that  kinetogenesis  is  more  potent  as  an  efficient  cause 
of  evolution  than  physiogenesis.  In  the  vegetable 
kingdom  it  is  quite  evident  that  evolution  is  more 
usually  physiogenetic  than  kinetogenetic.  Atmospheric 
and  terrestrial  conditions  play  a  major  role  in  the 

1  "  The  Energy  of  Evolution,"  American  Naturalist,  March,  1894.  "  The 
Origin  of  Structural  Variations  "  in  New  Occasions,  Chicago,  May,  1894.  C.  H. 
Kerr  &  Co. 


226   PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

determination  of  plant-structure,  but  motion  has  also 
had  an  important  influence.  The  motion,  however, 
has  originated  in  small  degree  in  the  plant  itself,  but 
has  been  derived  from  without.  Some  importance 
must  be  ascribed  to  the  effects  of  winds,  but  the  prin- 
cipal source  of  the  especial  strains  to  which  plants 
have  been  subjected,  has  been  the  insect  world.  In- 
sects have  been  inhabitants  of  land-plants  since  their 
origin  in  early  Paleozoic  ages,  and  the  mutual  relations 
of  plants  and  insects  have  ever  been  intimate.  As  has 
been  insisted  by  Muller  and  Henslow,  the  uses  to 
which  the  floral  organs  have  been  put  by  hymenopte- 
rous  and  other  insects  have  been  probably  a  principal 
cause  of  the  forms  assumed  by  the  former.  From  this 
direction  has  been  derived  the  kinetogenetic  influence 
in  plant  evolution.  The  few  independent  movements 
displayed  by  plants  may  have  had  some  influence  on 
the  evolution  of  their  structure.  We  have  no  reason 
as  yet  to  suppose  that  such  movements  have  any  other 
than  purely  physical  factors. 


CHAPTER  V.— PHYSIOGENESIS. 


T)OTANISTS  and  gardeners  are  familiar  with  the 
JJ  effects  of  physical  causes  in  producing  modifica- 
tions in  the  characters  of  plants.  That  modifications 
so  produced  have  become  hereditary  is  known  to  be 
the  fact,  and  we  may  therefore  infer  that  the  evolution 
of  plant  forms  has  been  produced  in  large  degree  by 
similar  agencies  in  past  geological  ages.  Says  Hens- 
low:1  "M.  Carriere  raised  the  radish  of  cultivation, 
Raphanus  sativus  L. ,  from  the  wild  species,  R.  rapha- 
nistum  L.,  and  moreover  found  that  the  turnip-rooted 
form  resulted  from  growing  it  in  a  heavy  soil,  and  the 
long-rooted  one  in  a  light  soil.  Pliny  records  the  same 
fact  as  practised  in  Greece  in  his  day,  saying  that  the 
male  (turnip  form)  could  be  produced  from  the  female 
(long  form)  by  growing  it  in  a  "  cloggy  soil. "  The 
rule  may  be  laid  down  that  a  species  [of  plant]  may 
be  constant  as  long  as  its  environment  is  constant,  but 
no  longer.  I  have  changed  the  spiny  Ononis  spinosa 
L.,  the  rest-harrow,  both  by  cuttings  and  by  seed  into 
a  spineless  form,  undistinguishable  from  the  species 
O.  repens  L.  in  two  years  ;  but  it  would  have,  I  doubt 

1  Natural  Science ;  1894,  pp.  259-260. 


228    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

not,  at  once  reverted  to  the  O.  spinosa  if  I  had  re- 
planted it  on  the  poor  soil  from  which  I  took  it.  It 
seems,  therefore,  to  be  a  very  hazardous  and  fallacious 
method  of  testing  the  value  of  specific  or  other  char- 
acters by  cultivation.  A  wild  plant  may  or  may  not 
change  at  once.  Thus  the  carrot,  Daucus  carota  L., 
proved  refractory  with  Buckman,  but  not  with  Vilmo- 
rin,  who  converted  this  annual  into  a  hereditary  bien- 
nial by  sowing  the  seed  late  in  the  season,  till  the 
character  of  flowering  in  the  second  season  became 
fixed." 

The  prevalence  of  spinous  plants  in  dry  and  desert 
regions  has  often  been  described.1  The  same  is  true  of 
reptiles,  although  spines  appear  on  some  species  in 
fertile  regions.  Spines  of  plants  are  believed  to  be 
twigs,  petioles,  leaves,  etc.,  partially  aborted  under  the 
influence  of  drought,  or  the  absence  of  the  water  neces- 
sary to  the  tissues  of  the  parts  in  question.  Wallace 
points  out,  however,  that  there  are  spinous  plants  in 
humid  climates,  citing  the  Gleditschia  (honey  locust) 
as  an  example.  The  spines  of  such  plants  may  be  sur- 
vivals of  periods  of  drought  in  previous  geologic  ages. 
Or  desiccation  of  certain  parts  of  a  plant  might  be  a 
form  of  abortion  of  those  parts,  a  phenomenon  which 
is  confined  to  no  region,  and  is  evidently  due  to  causes 
other  than  drought  in  some  cases.  Henslow  (/.  <r.) 
says  :  "They  [spines]  originate,  I  maintain,  as  a  mere 
accidental  and  inevitable  result  of  the  arrest  of  the 
organ  in  question,  such  arrest  being  mainly  due  to 
drought." 

One  of  the  best  expositions  of  the  influence  of  the 
physical  characters  of  the  environment  on  the  struc- 
ture of  animals  is  to  be  found  in  Semper's  work,  Ani- 

1  Natural  Science,  1894,  September,  p.  179. 


PHYSIOGENESIS.  229 

mat  Life,  to  which  I  refer  my  readers  for  a  fuller  ex- 
position than  can  be  given  here. 

a.   Relation  of  the  Size  of  Shells  of  Mollusca  to  the  En 

vironment. 

It  has  been  observed  that  both  in  natural  condi 
tions  and  in  confinement,  shells  of  fresh-water  Mol- 
lusca grow  to  a  larger  size  in  larger  bodies  of  water, 
and  become  reduced  in  size  as  the  bulk  of  water  in 
which  they  live  is  reduced.  Varigny  has  shown  that 
the  reduced  size  follows  a  reduction  of  the  air-surface 
of  the  water  rather  than  a  reduction  of  the  actual  bulk, 
though  the  two  conditions  may  often  coincide.  He 
also  shows  that,  other  things  being  equal,  the  size  of 
individuals  is  inversely  as  their  numbers  in  a  given 
enclosure. 

b.    The  Conversion  of  Artemia  Into  Branchinecta.^ 

In  1871  the  spring  flood  broke  down  the  barriers 
separating  the  two  different  lakes  of  the  salt  works 
near  Odessa,  diluting  the  water  in  the  lower  portion 
to  8°  Beaume",  and  also  introducing  into  it  a  large 
number  of  the  brine  shrimp,  Artemia  salina.  After  the 
restoration  of  the  embankment,  the  water  rapidly  in- 
creased in  density,  until  in  September,  1874,  it  reached 
25°  of  Beaum^'s  scale,  and  began  to  deposit  salt.  With 
this  increase  in  density,  a  gradual  change  was  noticed 
in  the  characters  of  the  Artemiae,  until  late  in  the 
summer  of  1874  forms  were  produced  which  had  all 
the  characters  of  a  supposed  distinct  species,  A.  muel- 
hausenii.  The  reverse  experiment  was  then  tried.  A 
small  quantity  of  the  water  was  then  gradually  diluted, 

1  Abstracted  from  an  account  by  J.  S.  Kingsley,  Standard  Natural  His- 
tory, Vol.  II. 


230    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

by  M.  Vladimir  Schmankewitsch,  who  conducted  the 
experiments,  and  though  continued  for  only  a  few 
weeks,  a  change  in  the  direction  of  A.  salina  was  very 
apparent.  Led  by  these  experiments,  he  tried  still 
others.  Taking  Artemia  salina,  which  lives  in  brine  of 
moderate  strength,  he  gradually  diluted  the  water,  and 
obtained  as  a  result  a  form  which  is  known  as  Branchi- 
necta  schcefferii,  the  last  segment  of  the  abdomen  hav- 
ing become  divided  into  two.  Nor  is  this  change  pro- 
duced by  artificial  means  alone.  The  salt  pools  near 
Odessa,  after  a  number  of  years  of  continued  washing, 
became  converted  into  fresh-water  pools,  and  with  the 
gradual  change  in  character,  Artemia  salina  produced 
first  a  species  known  as  Branchinecta  spinosa,  and  at  a 
still  lower  density  Branchinecta  ferox,  and  another  spe- 
cies described  as  B.  media.  Here  not  only  new  species 
were  produced,  but  a  new  genus. 

c.    The  Production  of  Colors  in  Lepidopterous  Pupcz. 

The  following  important  contribution  to  this  sub- 
ject has  been  made  by  Poulton.1  As  an  illustration  of 
the  direct  effect  of  the  environment  in  the  production 
of  color-changes,  it  is  of  the  greatest  value.  Several 
lepidopterists,  among  others  Weismann  and  Merrifield, 
had  shown  that  by  exposing  the  pupae  of  butterflies  to 
low  temperatures  material  changes  in  the  coloration 
of  the  mature  insects  can  be  produced.  Says  Poulton: 
"In  1867  Mr.  T.  W.  Wood  exhibited  to  the  Entomo- 
logical Society  of  London  a  number  of  chrysalides  of 
the  large  and  small  garden  white  butterflies  (Pieris 
brassica  and  P.  rapce],  which  corresponded  in  color  to 
the  surfaces  to  which  they  were  attached.  Dark  pupae 

1  The  Colors  of  Animals,  International  Scientific  Series,  Vol.  LXVIII,  by 
E.  B.  Poulton,  London,  1890. 


PH  YSIOGENESIS.  23 1 

had  been  found  on  tarred  fences  and  in  subdued  light ; 
light  ones  on  light  surfaces  ;  while  green  leaves  were 
shown  to  produce  green  chrysalides,  at  any  rate  in  cer- 
tain cases. 

"During  the  following  nineteen  years,  gradual  con- 
firmation of  Mr.  Wood's  central  position  was  afforded. 
In  1873  Professor  Meldola  supported  the  observations 
upon  the  chrysalides  of  the  "garden  whites. "  He 
compared  large  numbers  of  individuals  and  found  that 
the  pupae  upon  black  fences  were  darker  than  those 
upon  walls. 

"In  1874  a  paper  by  Mrs.  M.  E.  Barber,  and  com- 
municated by  Mr.  Darwin  to  the  Entomological  So- 
ciety of  London,  was  printed  in  the  transactions  of 
that  society.  Mrs.  Barber  had  experimented  with  a 
common  South  African  swallow-tailed  butterfly  (Papi- 
llanireus*),  and  had  found  the  chrysalis  wonderfully 
sensitive  to  the  colors  of  its  environment.  When  the 
pupae  were  attached  among  the  deep  green  leaves  of 
the  food-plant,  orange,  they  were  of  a  similar  color ; 
when  fixed  to  dead  branches  covered  with  withered, 
pale,  yellowish-green  leaves,  they  resembled  the  latter. 
One  of  the  caterpillars  affixed  itself  to  the  wood  frame 
of  the  case,  and  then  became  a  yellowish  pupa  of  the 
same  color  as  the  wooden  frame. 

"Mr.  Maurel  Weale  also  showed  that  the  color  of 
certain  other  South  African  pupae  can  be  modified,  and 
Mr.  Roland  Trimen  made  some  experiments  upon  an- 
other African  swallow-tail  (Papilio  demoleus}  confirm- 
atory of  Mrs.  Barber's  observations.  He  covered  the 
sides  of  the  cage  with  bands  of  many  colors,  and  found 
that  green,  yellow,  and  reddish-brown  tints  were  re- 
sembled by  the  pupae,  while  black  made  them  rather 
darker.  Bright  red  and  blue  had  no  effect.  The  larvae 


232    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

did  not  exercise  any  choice,  but  fixed  themselves  in- 
discriminately to  colors  which  their  pupa  could  re- 
semble and  those  which  they  could  not.  In  the  nat- 
ural conditions  the  latter  would  not  exist,  for  the  pupae 
can  imitate  all  the  colors  of  their  normal  environ- 
ments. 

"I  began  work  with  the  common  peacock  butter- 
fly (  Vanessa  io),  of  which  the  chrysalis  appears  in  two 
forms,  being  commonly  dark  gray,  but  more  rarely, 
bright  yellowish-green  ;  both  forms  are  gilded,  espe- 
cially the  latter.  Only  six  caterpillars  could  be  obtained, 
and  these  were  placed  in  glass  cylinders  surrounded  by 
yellowish-green  tissue-paper.  Five  of  them  became 
chrysalides  of  the  corresponding  color  ;  the  sixth  was 
removed  immediately  after  the  caterpillar  skin  had  been 
thrown  off,  and  was  placed  in  a  dark  box  lined  with 
black  paper,  but  it  subsequently  deepened  into  a  green 
pupa  exactly  like  the  others.  Obviously  the  surround- 
ings had  exercised  their  influence  before  the  pupa  was 
removed. 

"  Being  unable  to  attain  more  larvae  of  the  pea- 
cock, I  worked  upon  the  allied  small  tortoise-shell 
butterfly  (Vanessa  urtiaz),  which  can  be  obtained  in 
immense  numbers.  In  the  experiments  conducted  in 
1886,  over  seven  hundred  chrysalides  of  this  species 
were  obtained  and  their  colors  recorded.  Green  sur- 
roundings were  first  employed  in  the  hope  that  a  green 
form  of  pupa,  unknown  in  the  natural  state,  might  be 
obtained.  The  results  were,  however,  highly  irregular, 
and  there  seemed  to  be  no  susceptibility  to  the  color. 
The  pupae  were,  however,  somewhat  darker  than  usual, 
and  this  result  suggested  a  trial  of  black  surroundings, 
from  which  the  strongest  effects  were  at  once  wit- 
nessed :  the  pupae  were  as  a  rule  extremely  dark,  with 


PHYSIOGENESIS.  233 

only  the  smallest  trace,  and  often  no  trace  at  all,  of  the 
golden  spots  which  are  so  conspicuous  in  the  lighter 
forms.  These  results  suggested  the  use  of  white  sur- 
roundings, which  appeared  likely  to  produce  the  most 
opposite  effects.  The  colors  of  nearly  one  hundred 
and  fifty  chrysalides  obtained  under  such  conditions 
were  very  surprising.  Not  only  was  the  black  color- 
ing matter  as  a  rule  absent,  so  that  the  pupa?  were 
light-colored,  but  there  was  often  an  immense  devel- 
opment of  the  golden  spots,  so  that  in  many  cases  the 
whole  surface  of  the  pupae  glittered  with  an  apparent 
metallic  lustre.  So  remarkable  was  the  appearance 
that  a  physicist,  to  whom  I  showed  the  chrysalides, 
suggested  that  I  had  played  him  a  trick  and  had  cov- 
ered them  with  gold-leaf. 

"These  remarkable  results  led  to  the  use  of  a  gilt 
back-ground  as  even  more  likely  to  produce  and  in- 
tensify the  glittering  appearance.  By  this  reasoning 
I  was  led  to  make  the  experiment  which  had  been  sug- 
gested by  Mr.  Wood  nineteen  years  before.  The  re- 
sults quite  justified  the  reasoning,  for  a  much  higher 
percentage  of  gilded  chrysalides,  and  still  more  re- 
markable individual  instances,  were  obtained  among 
the  pupae  which  were  treated  in  this  way. 

"These  observations  and  experiments  had  been 
made  when  I  began  to  work  at  the  subject  in  1886: 
they  appeared  to  prove  that  the  power  certainly  exists, 
but  nothing  was  really  known  as  to  the  manner  in 
which  the  adjustment  is  effected.  Mr.  S.  W.  Wood's 
original  suggestion,  that  the  '  skin  of  the  pupa  is  pho- 
tographically sensitive  for  a  few  hours  only  after  the 
caterpillar's  skin  has  been  shed,'  was  accepted  by  most 
of  those  who  had  worked  at  the  subject.  And  yet  the 
suggestion  rested  upon  no  shadow  of  proof ;  it  de- 


234    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

pended  upon  a  tempting  but  overstrained  analogy  to 
the  darkening  of  the  sensitive  photographic  plate  un- 
der the  action  of  light.  But  the  analogy  was  unreal, 
for,  as  Professor  Meldola  stated  in  the  discussion  which 
followed  Mrs.  Barber's  paper,  <  the  action  of  light  upon 
the  sensitive  skin  of  a  pupa  has  no  analogy  with  its 
action  on  any  known  photographic  chemical.  No 
known  substance  retains  permanently  the  color  re- 
flected on  it  by  adjacent  objects.'  The  supposed  'pho- 
tographic sensitiveness '  of  chrysalides  was  one  of  those 
deceptively  feasible  suggestions  which  are  not  tested 
because  of  their  apparent  probability.  It  would  have 
been  very  easy  to  transfer  a  freshly  formed  pupa  from 
one  color  to  another  which  is  known  to  produce  an 
opposite  effect  upon  it ;  and  yet  if  this  simple  experi- 
ment had  been  made  the  theory  would  have  collapsed, 
for  the  pupa  would  have  been  found  to  resemble  the 
first  color  and  not  the  second.  Furthermore,  Mr. 
Wood's  suggestion  raised  the  difficulty  that  chrysa- 
lides which  had  become  exposed  in  the  course  of  a 
dark  night  would  have  no  opportunity  of  resembling 
the  surrounding  surfaces,  for  the  pupal  colors  deepen 
very  quickly  into  their  permanent  condition. 

"Having  thus  defined  the  time  of  susceptibility, 
the  next  question  was  to  ascertain  the  organ  or  part  of 
the  larva  which  is  sensitive.  At  first  it  appeared 
likely  that  the  larvae  might  be  influenced  through  their 
eyes  (ocelli),  of  which  they  have  six  on  each  side  of 
the  head.  Hence,  in  many  experiments  the  eyes  of 
some  of  the  larvae  were  covered  with  an  innocuous 
black  opaque  varnish,  and  they,  together  with  an  equal 
number  of  normal  larvae  from  the  same  company,  were 
placed  in  gilt  or  white  surroundings.  The  pupae  from 
both  sets  of  larvae  were,  however,  always  equally  light- 


PHYSIOGENESIS.  235 

colored.  It  then  seemed  possible,  although  highly  im- 
probable, that  the  varnish  itself  might  act  as  a  stimulus 
similar  to  that  caused  by  gilt  or  white  surroundings, 
and  therefore  the  experiments  were  repeated  with  black 
surroundings  in  darkness,  but  the  pupae  of  the  two  sets 
were  again  almost  identical,  so  that  it  appeared  cer- 
tain that  the  eyes  can  have  nothing  to  do  with  the  in- 
fluence. 

"  It  then  seemed  possible  that  the  large  branching 
bristles,  with  which  the  larvae  are  covered,  might  con- 
tain some  organ  which  was  affected  by  surrounding 
colors,  but  experiments  in  which  half  of  the  larvae  were 
deprived  of  their  bristles  showed  conclusively  that  the 
sensitive  organs  must  have  some  other  position,  for 
the  pupae  from  both  sets  of  larvae  were  identical. 

"  I  was  thus  driven  to  the  conclusion  that  the  gen- 
eral surface  of  the  skin  of  the  caterpillar  is  sensitive  to 
color  during  stage  ii,  and  part  of  stage  iii.  In  order 
to  test  this  conclusion,  I  wished  to  subject  the  body  of 
the  same  larvae  to  two  conflicting  colors,  such  as  black 
and  gold,  producing  the  most  opposite  effects  upon 
the  pupa.  Such  an  experiment,  if  successfully  carried 
out,  would  decide  some  important  points.  If  the  part 
of  the  body  containing  the  head  was  not  more  sensi- 
tive than  the  other  part,  a  valuable  confirmation  of  the 
blinding  experiments  would  be  afforded.  Mrs.  Bar- 
ber's suggestion  that  particolored  pupae  may  be  pro- 
duced by  the  influence  of  two  colors  would  be  tested 
in  a  very  complete  manner  ;  if  particolored  pupae  were 
obtained,  it  seemed  probable  that  the  light  acts  di- 
rectly upon  the  skin,  but  if  they  could  not  be  obtained, 
it  seemed  more  probable  that  the  light  influences  the 
termination  of  nerves  in  the  skin,  and  that  the  pupal 
colors  are  produced  through  the  medium  of  the  nervous 


236    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

system.  The  experiments  were  conducted  in  two 
ways.  In  the  first,  the  larvae  were  induced  to  suspend 
themselves  from  sheets  of  clear  glass,  by  placing  them 
in  wide  shallow  boxes,  so  that  the  ascent  to  the  glass 
roof  was  easily  accomplished.  As  soon  as  suspension 
(stage  iii.)  had  taken  place,  each  larva  was  covered 
with  a  cardboard  tube,  divided  into  two  chambers  by 
a  horizontal  partition,  which  was  fixed  rather  below 
the  middle.  There  was  a  central  hole  in  the  partition 
just  large  enough  to  admit  the  body  of  the  larva.  The 
tube  was  fixed  to  the  glass  sheet  with  glue  ;  the  upper 
chamber  was  lined  with  one  color,  e.  g.  gilt,  and  the 
lower  chamber  with  the  opposite  color,  e.  g.  black, 
with  which  the  outside  of  the  cylinder  was  also  cov- 
ered, in  case  the  larva  should  stretch  its  head  beyond 
the  lower  edge.  The  partition  was  fixed  at  such  a 
height  that  the  larval  head  and  rather  less  than  half  of 
the  total  surface  of  skin  were  contained  in  the  lower 
chamber,  while  rather  more  than  half  of  the  skin  sur- 
face was  contained  in  the  upper  chamber. 

"The  second  method  of  conducting  the  conflicting 
color  experiments  was  superior  in  the  more  equal  illu- 
mination of  the  upper  and  lower  colors.  The  bottom 
of  a  shallow  wooden  box  was  covered  with  alternate 
areas  of  black  and  gilt  papers,  and  partitions  were 
fixed  along  the  lines  where  the  two  colors  c'ame  in 
contact.  Each  partition  was  gilt  toward  the  gilt  sur- 
face, and  black  toward  the  black  surface,  and  was  per- 
forated close  to  the  bottom  of  the  box  with  holes  that 
would  just  admit  the  body  of  a  larva.  The  box  was 
th,en  placed  in  a  vertical  position  towards  a  strong 
light,  so  that  the  partitions  became  strong  shelves, 
while  the  black  and  gilt  surfaces  were  uppermost  alter- 
nately. As  soon  as  a  larva  was  suspended  to  a  glass 


PHYSIOGENESIS.  237 

sheet,  the  boss  of  silk  was  carefully  scraped  off  and 
was  pinned  on  the  upper  color,  above  one  of  the  holes, 
so  that  the  head  and  first  five  body-rings  passed 
through  the  hole  on  to  the  color  beneath,  which  tended 
to  produce  opposite  effects.  Other  larvae  were  simi- 
larly fixed  between  the  shelves  upon  one  color  only,  so 
as  to  afford  a  comparison  with  the  results  of  the  con- 
flicting colors. 

"A  careful  comparison  of  all  the  pupae  obtained  in 
the  conflicting  color  experiments  showed  that,  when 
the  illumination  of  the  two  surfaces  was  equal,  the  ef- 
fective results  were  produced  by  that  color  to  which 
the  larger  area  of  skin  had  been  exposed,  whether  the 
head  formed  part  of  that  area  or  not.  Particolored 
pupae  were  never  obtained.  It  therefore  appears  to  be 
certain  that  the  skin  of  the  larva  is  influenced  by  sur- 
rounding colors  during  the  sensitive  period,  and  it  is 
also  probable  that  the  effects  are  wrought  through  the 
medium  of  the  nervous  system.  The  latter  conclu- 
sion receives  further  confirmation  from  other  observa- 
tions." 

Professor  Poulton  has  since  produced  remarkable 
color-changes  in  the  larvae  of  Lepidoptera  by  confin- 
ing them  to  the  branches  of  plants  of  distinct  colors. 
Thus  geometrid  larvae  confined  to  the  stems  of  a  black 
color,  became  correspondingly  dark ;  while  those  re- 
stricted to  white  twigs  became  very  pale.  Jhese  larvae, 
and,  still  more  strikingly,  those  of  Cossus  ligniperda, 
when  confined  on  branches  which  supported  lichens, 
became  of  variegated  colors,  corresponding  with  those 
of  the  lichens,  and  affording  an  admirable  means  of 
concealment. 


238    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

d.    The  Effect  of  Light  on  the  Colors  of  Flatfishes. 

It  is  well  known  that  the  side  of  the  body  which  is 
uppermost  in  the  normal  position  in  the  flatfishes 
(Pleuronectidae)  is  colored  generally  with  dark  tints, 
and  frequently  with  a  distinct  pattern,  while  the  lower 
side  is  white.  This  is  due  to  the  absence  from  the 
lower  side  of  the  chromatophorae  or  pigment-contain- 
ing cells,  which  are  abundant  on  the  upper  side.  The 
young  fish  has  chromatophorae  on  both  sides  as  it  has 
its  eyes  also  in  the  normal  position,  but  as  the  fish 
turns  the  left  side  upwards  and  the  right  eye  gradually 
rotates  to  the  left  side,  the  chromatophorae  disappear 
from  the  right  side,  which  thus  becomes  colorless. 

Prof.  J.  T.  Cunningham1  experimented  with  young 
flounders  taken  at  the  beginning  or  middle  of  their 
metamorphosis,  by  placing  a  mirror  below  the  aqua- 
rium in  which  they  were  kept,  at  an  angle  of  45°,  and 
cutting  off  the  light  from  above  by  an  opaque  cover. 
In  the  great  majority  of  the  specimens  treated  in  this 
way,  after  several  months,  although  no  effect  was  pro- 
duced upon  the  eyes,  more  or  less  of  the  skin  of  the 
lower  side  was  pigmented.  He  thus  showed  that  the 
absence  of  pigment  on  that  side  in  the  normal  fish  is 
due  to  its  position  in  shadow,  where  little  light  can 
reach  it. 

e.    The  Effect  of  Feeding  on  Color  in  Birds. 
Mr.  F.  E.  Beddard  cites  the  following  remarkable 
example  of  the  direct  effect  of  internal  physical  causes 
in  producing  change  of  coloration.2 

1  Zoologischer  Anzeiger,  1891. 

2  Animal  Coloration,  an  Account  of  the  Principal  Facts  and  Theories  Relat- 
ing to  the  Colors  and  Markings  of  Animals.     By  Frank   E.  Beddard,  M.  A. 
Cxon.,  F.  R.  S.  E.     With  Four  Colored  Plates;  and  Wood-Cuts  in  the  Text. 
London  .  Swan  Sonnenschein  &  Co.     New  York  :  Macmillan  &  Co.     1892. 


PHYSIOGENESIS.  239 

'  *  That  the  yellow  color  of  canaries  can  be  altered 
to  an  orange  red  by  mixing  cayenne  pepper  with  their 
food,  has  been  known  for  a  long  time.  This  curious 
fact  was  first  discovered  in  England,  as  was  also  the 
fact  that  the  different  races  of  canaries  vary  in  their 
susceptibility  to  the  action  of  the  pepper  ;  some  kinds 
are  more,  others  are  less,  affected,  while  one  race  is 
absolutely  without  any  power  of  having  its  coloration 
altered  by  these  means.  The  color-change  is  pro- 
duced by  feeding  the  newly  hatched  young  with  the 
pepper  conveyed  in  their  food  or  the  old  birds  while 
sitting  upon  the  nest  are  furnished  with  food  contain- 
ing the  cayenne,  which  they  in  turn  feed  their  offspring. 
The  color  change  can,  in  fact,  be  only  brought  about 
in  very  young  birds  whose  feathers  are  not  completely 
matured  ;  it  is  quite  impossible  to  produce  any  altera- 
tion upon  the  full-grown  canary.  Clearly,  therefore, 
here  is  an  instance  of  the  direct  effect  of  food  upon 
color.  An  interesting  paper  upon  the  subject,  which 
has  also  furnished  me  with  the  facts  already  men- 
tioned, has  lately  appeared,1  and  it  will  be  of  interest 
to  give  some  account  of  the  author's  (Dr.  Sauermann's) 
experiments  for  reasons  that  will  appear.  Cayenne 
pepper,  of  course,  is  a  composite  substance,  from  which 
a  number  of  distinct  chemical  substances  can  be  ex- 
tracted :  the  red  color  is  caused  by  a  pigment  termed 
capsicin,  which  can  be  separated  from  the  pepper  ; 
and  it  might  easily  be  supposed  that  the  change  from 
yellow  to  red  in  the  feathers  of  the  canary  was  simply 
caused  by  a  transference  of  the  pigment,  as  in  the 
cases  mentioned  on  page  127;  but  Dr.  Sauermann 
shows  that  it  is  not  so.  Yellow-colored  canaries  were 

\Archiv fur  Anatotnie  und  Physiologic.  1889.  Physiologische  Abtheilung, 
543- 


240    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

not  in  the  very  slightest  degree  affected  by  the  pig- 
ment alone ;  but,  curiously  enough,  particolored  birds 
did  react, — the  brown  parts  of  the  feathers  became 
distinctly  lighter  in  hue.  It  is  a  fatty  substance  (trio- 
lein)  which  appears  to  convey  the  pigment,  and  to  pro- 
duce thus  a  changing  of  the  color  from  yellow  to  red  ; 
and  further  experiments  were  made  with  other  birds, 
showing  that  it  is  not  only  canaries  which  are  influenced 
by  their  food  in  this  way.  Some  white  fowls,  belong- 
ing to  a  special  breed,  showed  traces  of  yellow  among 
the  feathers  after  feeding  with  cayenne  ;  but  in  this 
case  there  were  not  racial  but  individual  differences  in 
susceptibility,  for  all  the  specimens  of  birds  experi- 
mented with  did  not  react  to  the  stimulus. 

"  A  similar  series  of  experiments  was  made  with 
some  other  colors  :  it  was  found  with  carmine  that  the 
yellow  color  was  destroyed  and  the  birds  became  white. 
This  unexpected  effect  is  explained  by  the  fact  that  a 
mixture  of  violet  and  yellow  produces  white.  The  fact 
that  the  fatty  constituent,  triolein,  plays  the  chief  part 
in  the  coloring  of  the  feathers  may  perhaps  help  to  ex- 
plain the  very  singular  fact  that  the  Amazon  parrots 
change  from  green  to  yellow  when  fed  upon  the  fat  of 
certain  fishes. 

"  With  regard  to  the  white  fowls  referred  to,  the 
experiments  made  by  Dr.  Sauermann  were  particularly 
interesting.  The  interest  lies  in  the  fact  that  the  pig- 
ment was  not  absorbed  equally  by  all  the  feathers  ; 
only  special  tracts  were  affected  ;  the  breast  feathers, 
for  instance,  became  red,  while  the  head  remained 
white.  It  is  therefore  quite  credible  that  in  a  state  of 
nature  partial  alteration  of  color  may  be  produced  by 
a  change  of  diet." 

In  a  chapter  of  Dr.  Beddard's  book  relating  to  pro- 


PHYSIOGENESIS.  241 

tective  resemblances  will  be  found  an  account  of  sev- 
eral examples  of  animals  which  have  apparently  ac- 
quired a  resemblance  to  their  surroundings  by  the 
transference  of  pigment  to  their  bodies  in  their  food. 

f.    The  Blindness  of  Cave- Animals. 

Neo-Lamarckian  writers  have  always  ascribed  the 
absence  or  rudimentary  condition  of  the  eyes  charac- 
teristic of  animals  which  dwell  exclusively  in  caves,  to 
disuse  consequent  on  the  absence  of  light.  Lamarck 
ascribed  the  rudimentary  condition  of  the  eyes  in  the 
mole  to  this  cause.  As  the  removal  of  so  important 
an  organ  as  the  eye  is  not  accomplished  in  a  single 
generation,  the  element  of  heredity  enters  the  propo- 
sition. This  subject  is  reserved  for  Part  Third  of  this 
book  ;  nevertheless,'  for  the  present  suspending  judg- 
ment as  to  this  question,  it  has  been  rendered  exceed- 
ingly probable  by  embryological  investigations  into  the 
history  of  dwellers  in  darkness,  that  the  Neo-Lamarck- 
ian view  is  the  correct  one.1  Says  Packard  : 

* '  In  my  essay  on  The  Cave  Fauna  of  North  America 
(p.  139),  I  record  the  fact  that  in  the  young  of  the 
blind  crayfish  (Orconectcs  pellucidus},  the  eyes  of  the 
young  are  perceptibly  larger  in  proportion  to  the  rest 
of  the  body  than  in  the  adult,  the  young  specimen  ob- 
served being  about  half  an  inch  in  length.  Previously 
to  this,  Dr.  Tellkampf,  in  1844,  remarked  that  'the 
eyes  are  rudimentary  in  the  adults,  but  are  larger  in 
the  young.'  Mr.  S.  Garman  states,  regarding  the  blind 
Cambarus  of  the  Missouri  Cave  :  'Very  young  speci- 
mens of  C.  setosus  correspond  better  with  the  adults  of 
C.  bartonii;  their  eyes  are  more  prominent  in  these 

H  am  indebted  for   a  rtsuniS  of  this  subject  to  Packard,  American  Nat- 
uralist, 1884,  p.  735. 


242    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

stages,  and  appear  to  lack  but  the  pigment.'  In  the 
blind  cave-shrimp  (Troglocaris)  of  Austria,  Dr.  Joseph 
discovered  that  the  embryo  in  the  egg  is  provided  with 
eyes. 

"  In  this  connection  should  be  recalled  the  observa- 
tions of  Semper  in  his  Animal  Life  (pp.  80,  81)  on  Pin- 
notheres holothurice,  which  lives  in  the  '  water-lungs ' 
of  holothurians,  where,  of  course,  there  is  an  absence 
of  light.  The  zoea  of  this  form  has  large  '  well-de- 
veloped eyes  of  the  typical  character.  Even  when 
they  enter  the  animal  they  still  preserve  these  eyes ; 
but  as  they  grow  they  gradually  become  blind  or  half- 
blind,  the  brow  grows  forward  over  the  eyes,  and 
finally  covers  them  so  completely  that,  in  the  oldest 
individuals,  not  the  slightest  trace  of  them,  or  of  the 
pigment,  is  to  be  seen  through  the  thick  skin,  while, 
at  the  same  time,  the  eyes  seem  to  undergo  a  more  or 
less  extensive  retrogressive  metamorphosis.' 

"In  this  connection  may  be  mentioned  the  case  of 
the  burrowing  blind  shrimp  (Callianassa  stimpsonii), 
which  has  been  found  by  Prof.  H.  C.  Bumpus,  at 
Wood's  Holl,  Mass.,  living  in  holes  at  a  depth  of  be- 
tween one  and  two  feet.  He  has  kindly  given  me  a 
specimen  of  the  shrimp,  which  is  blind,  with  reduced 
eyes,  smaller  in  proportion  to  the  body  than  those  of 
the  blind  crayfish.  He  has  also  obtained  the  eggs, 
and  has  found  that  the  embryos  are  provided  with  dis- 
tinct black,  pigmented  eyes,  which  can  be  seen  through 
the  egg-shell. 

"Recently,  Zeller  has  studied  the  embryology  of  the 
Proteus  of  Adelsberg  Cave,  and  has  confirmed  the 
statement  of  Michahelles,  who,  in  1831,  discovered 
that  the  eyes  of  this  animal  are  more  distinct  in  the 


PHYSIOGENESIS.  243 

young  and  somewhat  larger  than  in  the  adult.  We 
quote  and  translate  from  Zeller's  account : 

"  l  The  development  of  the  eyes  is  very  remarkable  ; 
they  are  immediately  perceived  and  present  themselves 
as  small,  but  entirely  black  and  clearly  drawn  circular 
points,  with  a  slit  which  is  very  narrow,  and  yet,  at 
the  same  time,  well  defined,  and  which  penetrates 
from  the  lower  circumference  out  to  the  middle. 

"'Indeed,  one  can  hardly  doubt  that  this  astonish- 
ing development  of  the  eye  has  been  accomplished  by 
the  influence  of  light,  as  has  also  the  pigmentation  of 
the  skin,  the  reddish-white  ground-color  of  which  ap- 
pears thickly  studded  with  very  small  brownish- gray 
points  mixed  with  detached  white  ones,  over  the  upper 
surface  of  the  head  and  over  the  back,  down  over  the 
sides  of  the  yellowish  abdomen.  Even  on  the  edge  of 
the  fins  (Floss ens auni)  the  pigment  is  found.  On  the 
other  hand,  there  is  a  whitish  spot  over  the  snout,  as 
is  likewise  the  case  in  the  adult  creatures  which  have 
been  colored  by  the  light.  Both  the  under  surface  of 
the  head  and  the  entire  abdomen  are  shown  free  from 
pigment  like  the  limbs.  .  .  . 

'"I  cannot  specify  very  exactly  as  to  when  the  pig- 
mentation of  the  skin  begins,  but,  in  any  case,  it  is 
very  early,  and  often  earlier  that  the  first  beginning  of 
the  eyes  can  be  discovered.  The  latter  occurs  toward 
the  end  of  the  twelfth  week,  at  which  time  a  thin,  light 
gray  line,  which  still  appears  overgrown,  may  be  per- 
ceived, forming  a  half-circle,  open  underneath.  Then 
while  this  line  subsequently  becomes  clearer  and 
darker,  and  its  ends  grow  further  under  and  towards 
each  other,  there  also  takes  place  simultaneously  a 
progression  of  the  pigment  larger  towards  the  middle 
point,  and  the  circle  finally  seems  closed  and  filled  up 


244    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

to  the  narrow  slit  mentioned  above,  which  proceeds 
from  the  lower  circumference  and  penetrates  to  the 
middle  of  the  eye'  (pp.  570,  571). 

1  'But  the  most  striking  discovery  bearing  on  this 
subject  is  that  of  the  condition  of  the  eyes  in  the  em- 
bryo and  young  compared  with  the  adult  of  the  blind 
goby  of  San  Diego. 

"In  his  essay  on  The  Fishes  of  San  Diego,  Professor 
Eigenmann  briefly  refers  to  and  gives  four  figures 
(Fig.  55)  of  the  embryo  of  Typhlogobius,  Mr.  C.  L. 
Bragg  having  been  fortunate  enough  to  discover  the 
egg  in  the  summer  of  1891.  'The  eyes  develop  nor- 
mally, and  those  of  No.  4  differ  in  no  way  from  the 
eyes  of  other  fish  embryos/  In  this  case,  then,  we 
have  the  simplest  and  clearest  possible  proof  of  the 
descent  of  this  blind  fish  from  individuals  with  eyes  as 
perfect  as  those  of  its  congeners. 

"We  have  been  permitted  by  the  Director  of  the 
United  States  National  Museum  to  reproduce  Profes- 
sor Eigenmann's  excellent  figures  on  .  the  embryo, 
which  tell  the  story  of  degeneration  of  the  eye  from 
simple  disease  of  the  organ,  the  species  being  exposed 
to  conditions  of  life  strikingly  different  from  those  of 
its  family  living  in  the  same  bay. 

"Before  the  discovery  of  the  eggs,  the  youngest  in- 
dividual ever  seen  is  represented  in  Fig.  55,  No.  i,  its 
eyes  being,  though  small,  yet  distinct,  and  'appar- 
ently functional.' 

"  From  these  data  it  is  obvious  that  future  embryo- 
logical  study  on  cave-animals  will  farther  demonstrate 
their  origin  from  ancestors  with  normal  eyes." 


CHAPTER  VI.— KINETOGENESIS. 


T  TNDER  the  head  of  kinetogenesis  (development  by 
LJ  motion)  comes  the  consideration  of  the  effect  of 
use  and  disuse.  Use  necessarily  conditions  the  evolu- 
tion of  useful  characters.  These  characters  are  such 
by  reason  of  their  adaptation  to  the  life-functions  of 
the  beings  which  possess  them.  It  is  perfectly  well 
known,  however,  that  all  plants  and  animals  possess 
more  or  less  numerous  peculiarities  which  are  not  use- 
ful to  their  possessors.  Such  are  the  mammae  of  male 
animals;  the  incisions  forming  palmate  or  pectinate 
leaves  and  petals  of  plants ;  rudimental  organs  of  all 
kinds  ;  great  elongation  of  the  vertebral  column,  espe- 
cially of  the  caudal  series  in  certain  species ;  patches 
of  color,  or  of  hairs,  at  particular  places,  etc.  These, 
and  many  others  may%be  arranged  in  divisions  accord- 
ing to  their  probable  origin,  as  follows : 

I.  Excess  of  growth  energy. 

Examples:    the  recurved  tusks  of  the  mammoth,  babirussa, 
etc. ;  the  elongate  feathers  of  some  birds,  etc. 

II.  Defect  of  growth-energy. 

i.  Atavism:  examples;  the  tritubercular   superior    molar  of 
certain  races  of  man. 


KINE  TO  GENESIS.  247 

2.  Degeneracy  from  disuse:  examples;  the    rudimental   legs 

and  digits  of  numerous  lizards. 

3.  Degeneracy  from  disuse  and  complementary  excess  else- 

where :  examples  ;  reduction  in  number  of  molars  and  in- 
cisors in  man  ;  reduced  mammae  in  male  Mammalia  ;  re- 
duction of  lateral  digits  in  the  true  horses  (Equus). 

4.  Physico-chemical  causes :  here  must  be  probably  included 

various  color-patches  and  color  tints,  for  which  no  other 
explanation  is  accessible. 

Darwin  considers  several  of  the  above  conditions, 
and  endeavors  to  explain  some  of  them  as  consequences 
of  natural  selection.  Equivalent  to  the  Section  I. 
above,  he  enumerates  extraordinary  developments  of 
particular  parts.1  He  says,  "A  part  developed  in  any 
species  in  an  extraordinary  degree  or  manner  in  com- 
parison with  the  same  part  in  an  allied  species,  tends 
to  be  highly  variable."  He  does  not  attempt  any  ex- 
planation of  the  origin  of  such  characters,  except 
through  natural  selection.  Of  the  characters  coming 
under  Section  II.  above,  he  says,  "  Multiple,  rudimen- 
tary and  lowly  organized  structures  are  variable."  Of 
these  he  remarks,  "  I  presume  that  lowness  here  means 
that  the  several  parts  of  the  organism  have  been  but 
little  specialized  for  particular  functions  ;  and  as  long 
as  the  same  part  has  to  perform  diversified  work,  we 
can  perhaps  see  why  it  should  remain  variable,  that 
is,  why  natural  selection  should  not  have  preserved  or 
rejected  each  little  deviation  of  form  so  carefully  as 
when  the  part  has  to  serve  for  some  one  special  pur- 
pose." Here  Mr.  Darwin  well  illustrates  his  unwilling- 
ness to  look  to  disuse  as  the  cause  of  the  conditions  he 
describes.  Under  "  Compensation  and  Economy  of 
Growth"  he  quotes  from  Goethe  that  "In  order  to 

ITAe  Origin  of  Species,  Ed.  1872,  p.  119. 


248    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

spend  on  one  side,  nature  is  forced  to  economize  on 
the  other  side."  I  have  expressed  the  same  view  in 
the  following  language  : 1 

"  The  complementary  diminution  of  growth-nutrition 
follows  the  excess  of  the  same  in  a  new  locality  or  or- 
gan, of  necessity,  if  the  whole  amount  of  which  an 
animal  is  capable  be,  as  I  believe,  fixed.  In  this  way 
are  explained  the  cases  of  retardation  of  character  seen 
in  most  higher  types.  The  discovery  of  truly  comple- 
mentary parts  is  a  matter  of  nice  observation  and  ex- 
periment." An  apparent  illustration  is  that  of  the  in- 
crease of  the  median  digits  in  the  diplarthrous  Ungu- 
lata  contemporaneously  with  the  diminution  and  atro- 
phy of  the  lateral  digits.  This  is,  however,  an  exam- 
ple of  the  relative  effects  of  use  and  disuse,  which  pro- 
ceed  contemporaneously,  and  it  is  probable  that  most 
if  not  all  cases  of  complementary  growth-relations  may 
be  expressed  in  this  way.  Thus  the  orthognathism  of 
the  higher  human  races  is  accompanied  by  full  frontal 
development,  the  two  modifications  constituting  a  re- 
tardation of  the  postembryonic  growth  of  the  face. 
But  this  change  can  be  traced  to  use,  increased  brain 
action  enlarging  that  organ,  and  expanding  its  osseous 
case,  probably  at  the  expense  of  lime  salts  which  would 
otherwise  go  to  the  jaws.  Reduction  of  teeth  in  Ar- 
tiodactyla  and  in  man  cannot  be  regarded  as  a  useful 
character  in  itself,  but  it  is  complementary  to  the  de- 
velopment of  other  characters  which  are  useful. 

Under  the  same  head  may  come  perhaps,  the  facts 
included  by  Mr.  Darwin  under  the  head  of  "  Correlated 
Variation."  Of  these  he  says,  "I  mean  by  this  ex- 
pression that  the  whole  organization  is  so  tied  together 

1 "  Method  of  Creation,"  Proceedings  of  the  American  Philosophical  Society, 
1871,  p,  257;  Origin  of  the  Fittest,  1887,  p.  201. 


KINETOGENESIS.  249 

during  its  growth  and  development,  that  when  slight 
variations  in  any  one  part  occur,  and  are  accumulated 
through  natural  selection,  other  parts  become  modi- 
fied." After  referring  to  various  characters  of  compo- 
site and  unbelliferous  plants  in  illustration  of  such  a 
law,  he  says  (/.  <:.,  p.  116),  "Hence  modifications  of 
structure,  viewed  by  systematists  as  of  high  value,  may 
be  wholly  due  to  the  laws  of  variation  and  correlation, 
without  being,  so  far  as  we  can  judge,  of  the  slightest 
service  to  the  species."  Here  Mr.  Darwin  admits  the 
insufficiency  of  natural  selection  as  an  explanation  of 
the  origin  of  such  characters;  for  he  says  (p.  119), 
"Natural  selection,  it  should  never  be  forgotten,  can 
act  solely  for  the  advantage  of  each  being."  He  goes 
further,  and  admits  (p.  114)  that  the  Lamarckian  doc- 
trine has  some  claims  to  credence,  where  he  says,  "On 
the  whole  we  may  conclude  that  habit,  or  use  and  dis- 
use, have  in  some  cases,  played  a  considerable  part  in 
the  modification  of  the  constitution  and  structure ;  but 
that  the  effects  have  often  been  largely  combined  with, 
and  sometimes  overmastered  by  the  natural  selection 
of  innate  variations." 


i.   KINETOGENESIS  OF  MUSCLE. 

The  fundamental  condition  of  the  molar  movements 
of  organic  beings  is  the  contractility  of  protoplasm.  In 
the  Amoeba  this  contractility  is  a  generally  diffused 
characteristic  of  its  body-substance,  and  this  is  the 
case  with  Rhizopoda  generally.  In  higher  Protozoa 
the  contractility  is  already  especially  developed  in  cer- 
tain regions  where  most  needed  for  the  movement  of 
the  body  in  definite  directions  ;  generally  immediately 
beneath  the  denser  sarcode  of  the  external  surface.  In 


250    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION, 

Stentor  this  substance  presents  the  appearance  of 
longitudinal  threads  ;  in  Gregarina  they  encircle  the 
body.  From  these  simple  beginnings  we  can  follow 
the  muscular  tissue  to  its  various  expressions  in  all 
classes  of  animals ;  to  the  concentric  threads  of  the 
Ccelenterata  ;  to  the  longitudinal  bundles  beneath  the 
integument  of  worms  ;  and  the  variously  directed 
masses  attached  to  the  external  skeleton  of  the  Arthro- 
poda,  and  the  internal  skeleton  of  the  Vertebrata.  The 
ease  with  which  muscular  tissue  is  grown  in  the  higher 
animals  under  use,  permits  us  to  infer  that  its  develop- 
ment in  all  animals  has  been  due  to  the  same  cause. 
Muscular  structure  is  directly  related  to  the  needs  of 
the  structures  to  which  it  is'  attached,  in  the  perform- 
ance of  movements.  In  rudimental  limbs  muscles  are- 
reduced  in  both  size  and  number,  distinct  slips  or 
bodies  becoming  fused.  In  enlarged  limbs  the  reverse 
process  takes  place.  Muscular  bellies  increase  in  size, 
and  in  number  by  subdivision.  The  muscular  system 
in  the  middle  and  higher  Vertebrata  is  variable,  and  its 
plasticity  to  the  stimuli  to  movements  is  well  known. 
It  is  evident  that  definite  muscular  bands  have  been 
developed  in  the  lines  of  resistance  which  it  has  been 
necessary  to  overcome  in  moving  the  body  or  parts  of 
it.  The  movable  segments  which  have  become  adapted 
for  contact  with  the  surrounding  media,  by  development 
of  hardness  or  extent  of  surface,  as  limbs  (feet,  wings), 
and  jaws,  have  naturally  become  the  points  of  origin 
of  the  most  efficient  muscular  bands.  No  one  can 
doubt  the  mutual  stimuli  which  the  muscular  ancl 
skeletal  systems  have  exchanged  during  the  process  of 
evolution,  since  they  are  necessary  to  each  other  from 
a  mechanical  point  of  view. 


KINE  TO  GENESIS.  25 1 

Huter,1  a  distinguished  specialist  in  the  diseases  of 
the  joints,  gives  the  following  positive  information  as 
to  the  easy  formation  of  new  modifications  of  muscu- 
lar structure : 

"Muscular  tissue  everywhere  possesses  the  capa- 
city to  shorten  itself  in  consequence  of  continued  ap- 
proximation of  its  points  of  insertion ;  that  is,  to  be- 
come shorter  by  the  disappearance  of  tissue,  in  pro- 
portion to  the  duration  of  the  approximation.  This 
law  is  of  the  greatest  importance  for  the  muscular  con- 
traction of  joints,  that  is,  for  such  restriction  of  the 
freedom  of  movement  of  the  articulations  as  has  its 
origin  in  muscular  movements.  We  have  experimen- 
tal opportunities  for  the  observation  of  this  fact,  such 
as  the  effect  of  a  stiff  bandage  on  an  articulation.  When 
it  is  necessary,  in  consequence  of  a  fracture  of  the  fore- 
arm, to  fix  the  elbow-joint  for  several  weeks  in  a  right- 
angled  flexure,  we  find  on  the  removal  of  the  bandage 
that  the  power  of  extension  of  the  fore-arm  has  been 
much  restricted.  That  the  cause  is  nutritive  change 
is  proven  by  the  fact  that  considerable  force  of  mus- 
cular contraction  is  necessary  before  the  normal  ex- 
tension can  be  effected." 

Similar  phenomena  are  to  be  observed  in  conse- 
quence of  a  prolonged  lying  in  bed,  where  no  injury 
to  the  innervation  exists. 

"The  muscles  adapt  themselves  to  the  permanent 
positions  of  the  articulations,  as  in  joint-contractions 
which  are  due  to  muscular  paralysis.  Those  muscles 
which  are  habitually  stretched,  increase  in  length, 
while  those  whose  insertions  are  approximated,  are 
shortened,  producing  joint-contraction."  He  then  goes 

1  Huter,  "  Studien  an  den  Extremitatengelenken  Neugeborener  und  Er- 
wachsener."     Virchow's  Archiv  f&r pathologische  Anatomie,  Bd.  XXV.,  6-8. 


252    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

on  to  describe  the  effect  of  such  fixation  of  joints  on 
the  bones  themselves,  to  which  I  will  refer  on  a  later 
page,  under  the  head  of  the  origin  of  articular  sur- 
faces. 

Professor  Eimer  of  Tubingen  has  given  us  a  synop- 
sis of  the  nature  of  the  evolution  of  the  characters  of 
the  muscular  tissue,  which  is  highly  instructive,  and 
of  which  I  present  here  an  abstract.1  The  conclusions 
reached  by  Eimer  are  derived  from  a  general  study  of 
the  subject,  both  in  the  laboratory  and  in  the  litera- 
ture. He  says  : 

"  (i)  It  is  apparently  continued  contractions  of  the 
protoplasm  in  definite  directions,  which  have  produced 
muscular  masses.  Since  plants  do  not  display  con- 
tinuous and  vigorous  movements,  they  have  not  de- 
veloped muscular  bodies. 

"(2)  Undoubted  facts  indicate  that  from  a  primi- 
tively identical  substance  muscular  tissue  has  devel- 
oped in  the  direction  of  effective  contractions,  while 
connective  tissue  has  developed  where  no  contractions 
have  been  present. 

"(3)  Muscle-masses  first  appeared  almost  every- 
where in  the  external  layer  of  the  contractile  region  : 
"a,  in  Protozoa  in  the  outer  layer  of  the  body; 
"  b>  in   Metazoa   in  the  tegumentary  sheath  of 

the  body. 

"  c,  They  consist  first  either  of  muscle-cells,  or 
muscle-fibers,  from  which  develop  man- 
tle muscle-cells  and  mantle  muscle-fibers. 
Mantle  muscle-fibers  compose  the  other- 
wise highly  developed  striped  muscles  of 

l"Die  Entstehung  und  Ausbildung  des  Muskelgewebes,  insbesondere 
der  Querstreifung  desselben  als  Wirkung  der  Thatigkeit  betrachtet."  Zeit- 
schrift  ftir  wissenschaftliche  Zoologie,  LIII.,  Suppl.,  1892,  p.  67. 


KINE  TO  GENESIS.  253 

Arthropoda,  and  some  Vertebrata  (Batra- 
chia).     And  when  the  entire  muscle-fiber  is 
divided  into  fibrillae,  there  can  appear  an 
external  layer  of  muscular  threads. 
"(4)  That  muscle  cells  and  fibers  first  appear  in 
the  external  stratum  of  the  active  body  of  animals,  is 
due  to  the  especially  active  movements  necessary  to 
this  part  of  the  body.      This   is  a  simple   mechanical 
consequence  of  the  fact,  that  in   a  more  or  less  longi- 
tudinally extended  body  of  protoplasm,  whether  it  be 
Protozoon  or  worm,  or  muscle-cell  or  muscle-fiber,  that 
its  movements  must  be  more  vigorous  on  the  external 
than  the  internal  portion  of  it.      Therefore,  the  former 
would  first  display  muscular  structure. 

"  (5)  If  the  first  stage  is  the  development  of  masses 
of  plasma,  which  display  contraction  in  definite  direc- 
tions, the  next  step  is  the  division  of  such  masses  into 
muscle-threads  or  fibrillae.  These  threads  must  be  re- 
garded as  a  result  of  contractions,  whose  inequality 
produces  subdivisions  of  the  original  mass.  A  com- 
pound structure  is  also  more  effective  than  a  simple 
one  in  effecting  contractions. 

"(6)  The  next  stage  of  evolution  of  muscular  tissue 
consists  of  the  appearance  of  the  cross-striping.  The 
mechanical  effect  of  the  cross-striping  is  to  distribute 
the  contractility  equally  throughout  the  length  of  the 
fiber.  The  contractions  of  the  unstriped  muscular 
fiber  are  less  vigorous,  and  also  less  uniformly  dis- 
tributed than  those  of  the  striped  fiber.  The  cross- 
striping  is  a  result  of  contractions.  It  commences  as 
simple  undulations  of  the  surface  of  the  fiber.  The 
contraction  of  the  plasma  is  wave-like  and  is  propa- 
gated rapidly  through  the  fiber,  and  is  not  due  to  a 
flow  and  return  of  the  contained  protoplasm.  The 


254 


PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


frequent  repetition  of  these  local  contractions  and  en- 
largement of  the  fiber  have  resulted  in  a  permanent 
difference  in  its  intimate  structure,  the  alternate  wavee 
becoming  fixed  as  cross-bands." 

As  evidence  of  the  truth  of  this  proposition,  (6), 
Eimer  cites  many  facts.  In  the  muscles  of  the  Mol- 
lusca,  striped  fibers  occur  in  those  forms,  as  Pecten, 
where  the  closing  of  the  shell  is  especially  vigorous, 
this  being  their  mode  of  progress  through  the  water. 
In  other  forms,  where  the  muscles  have  no  such  vigo- 
rous use,  the  fibers  are  smooth.  In  Arthropoda,  the 
muscles  of  the  legs  of  swiftly  running  forms  are  striped, 
while  those  of  the  alimentary  canal  are  smooth.  It  is 
a  general  law  that  muscles  which  have  energetic  con- 
tractions are  striped,  while  those  in  which  the  con- 
tractions are  slow  or  feeble,  are  smooth.  In  the  com- 
mon house-fly,  Eimer  records  some  remarkable  obser- 
vations. Flies  examined  in  winter,  during  the  period 
of  torpidity,  were  found  to  have  the  fibers  of  the  tho- 
racic muscles  smooth.  With  advance  of  the  spring 
the  striping  gradually  made  its  appearance,  and  in  the 
summer  it  was  fully  developed.  An  artificial  imitation 
of  winter,  by  refrigeration  in  an  ice-cellar,  caused  the 
cross-striping  to  disappear.  The  striping  in  some 
other  animals  is  shown  by  Eimer  to  be  strongly  in- 
fluenced by  physical  conditions. 

In  fact,  muscular  tissue  is  highly  plastic,  and  as  it 
is  directly  under  the  control  of  nervous  or  equivalent 
stimuli,  the  effect  of  the  latter  in  building  structure  is 
evident.  That  the  motion  communicated  to  the  hard 
parts  through  the  agency  of  the  muscular  system  is 
effective  in  building  the  hard  structures  will  be  shown 
in  a  subsequent  section. 


K2NE  TO  GENESIS.  255 


2.  KINETOGENESIS  IN  MOLLUSCA. 

a.    The  Origin  of  the  Plaits  in  the  Columella  of  the 
Gastropoda. 

Mr.  W.  H.  Dall  has  developed  the  mechanics  of 
evolution  in  the  Gastropoda,  and  I  quote  extracts  from 
one  of  his  papers  to  show  the  harmony  of  his  views 
with  those  of  other  Neo-Lamarckians.1  "The  question 
which  first  arises  is  as  to  the  origin  of  the  columellar 
plications  and  their  function.  In  considering  the  dy- 
namic relations  of  the  animal  to  its  shell  we  may  ob- 
tain satisfaction  on  this  point.  In  the  fusiform  Rha- 
chiglossa  an  anatomical  difference  exists  to  which  I 
believe  attention  has  not  hitherto  been  called.  In- 
deed, unless  the  principles  of  dynamic  evolution  are 
granted,  it  is  a  difference  which  would  appear  to  have 
little  or  no  significance.  These  principles,  however, 
afford  a  key  which  seems  to  unlock  this  and  many 
other  mysteries.  In  the  recent  forms  of  this  sort  the 
adductor  muscle,  which  in  all  gastropods  is  attached 
to  the  columella  at  a  certain  distance  within  the  aper- 
ture, is  attached  deeper  within  the  shell  than  in  non- 
plicate  forms.  The  point  of  attachment  may  be  an 
entire  turn,  or  even  more,  behind  the  aperture,  while 
in  short  globose  few-whorled  shells  and  in  the  non- 
plicate  forms  it  is,  as  a  general  rule,  little  more  than 
half  a  turn  behind  the  aperture. 

' '  Now  let  us  consider  the  dynamics  of  the  case.  We 
have,  reduced  to  its  ultimate  terms,  a  twisted,  shelly, 
hollow  cone,  subangulate  or  even  channelled  at  two  ex- 

1  Transactions  of  the  Wagner  Free  Institute  of  Science,  Philadelphia,  Aug., 
1890,  p.  58. 


256    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

tremes  corresponding  to  the  canal  and  the  posterior 
commissure  of  the  body  and  outer  lip.  Inside  of  this 
we  have  a  thin,  loose  epithelial  cone,  the  mantle,  of 
which  the  external  surface,  especially  toward  the  mar- 
gin, is  shell-secreting ;  lastly,  inside  of  the  mantle- 
cone  we  have  a  more  or  less  solid  third  cone,  consist- 
ing of  the  foot  and  other  external  parts  of  the  body  of 
the  animal,  which  can  be  extended  beyond  the  mantle- 
cone  outwardly,  as  the  mantle-cone  can  be  beyond  the 
shell- cone.  The  body-cone  and  the  mantle-cone  are 
attached  at  one  of  the  angles  of  the  shell-cone  some 
distance  within  the  opening  of  the  spiral  of  the  latter. 
The  two  outer  cones  constitute  a  loose,  flexible  funnel 
within  a  rigid,  inflexible  funnel,  while  the  body-cone 
forms  a  solid,  elastic  stopper  inside  of  all. 

"  What  will  happen  according  to  mechanical  prin- 
ciples (which  can  be  tested  by  anybody  with  the  sim- 
plest apparatus)  when  the  mantle-cone  is  withdrawn 
into  a  part  of  the  shell-cone  too  small  for  the  natural 
diameter  of  the  contracted  mantle-cone  ?  It  must 
wrinkle  longitudinally.  Where  will  the  wrinkles  come? 
They  will  come  at  the  angles  of  the  shell-cone  first ; 
they  will  be  most  numerous  toward  the  aperture,  since 
toward  the  aperture  the  mantle-cone  enlarges  dispro- 
portionately to  the  caliber  of  the  shell,  owing  to  its 
processes,  the  natural  fold  of  the  canal,  etc.,  etc.;  the 
deepest  and  strongest  wrinkles  will  be  on  the  pillar, 
owing  to  the  fact  that  the  attachment  of  the  adductor 
prevents  perfect  freedom  in  wrinkling  and  the  groove 
of  the  canal  will  mechanically  induce  the  first  fold  in 
that  vicinity.  The  most  numerous  small  wrinkles  will 
be  near  the  aperture  opposite  the  pillar,  because  of 
the  mantle-edge  this  is  the  most  expanded  part,  and 
there  will  be  a  tendency  to  a  ridge  near  the  angle  of 


KINE  TO  GENESIS. 


257 


the  posterior  commissure.  Repeated  dragging  of  a 
shell  secreting  surface,  thus  wrinkled,  over  a  surface 
fitted  to  receive  such  secretion,  will  result  in  the  ele- 
vated shelly  ridges  which  on  the  pillar  we  call  plica- 
tions ;  and  on  the  outer  lip  lirae,  if  long,  or  teeth,  if 
short.  The  commonly  existing  subsutural  internal 
ridge  on  the  body  of  the 
shell  near  the  posterior  com- 
missure will  mark  the  spe- 
cial conditions  in  that  part 
of  the  aperture. 

"When  the  secreting  sur- 
face is  thus  wrinkled  or  cor- 
rugated longitudinally,  the 
wrinkles  and  the  concave 
folds  between  them  will  be 
directed  in  the  sense  or  di- 
rection in  which  the  body 
moves  in  emerging  from  or 
withdrawing  to  the  whorl. 
The  summits  of  the  convex 
wrinkles  will  be  appressed 
more  or  less  forcibly  against 
the  shell -wall  exterior  to 
them  in  which  they  are  con- 
fined. The  semi-fluid,  limy  body  ..whorl  °pen*d'  ^spiayinR 

J      non-nhratft  rohimftlla.    From  Dall. 

secretion  of  which  the  shell- 
lining  is  built  up,  exuding  from  the  whole  surface  of 
the  mantle,  will  be  rubbed  away  from  the  lines  of  the 
summits  of  the  wrinkles  and  tend  to  accumulate  in 
lines  corresponding  to  the  concave  furrows  between 
the  wrinkles.  This  secretion  hardens  rapidly  and 
these  lines  would  become  somewhat  elevated  ridges 
which  would  by  their  presence  (when  once  initiated) 


Fig.  56. — Fusus  far  His  Con.  the 
y     whorl    opened,    displaying 
non-plicate  columella.    From  Dall. 


258    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

tend  to  maintain  the  furrows  and  wrinkles  in  the  same 
place  with  relation  to  the  thus-initiated  lirae,  as  these 
elevated  lines  are  called  when  on  the  outer  lip  ;  or 
plaits,  when  situated  on  the  pillar. 

"The  modification  referred  to  generally  takes  place 
during  resting  stages  of  the  animal's  growth,  since 
while  the  animal  is  rapidly  extending  its  coil  the  se- 
cretions seem  to  be  directed  toward  the  extreme  mar- 
gin, and  the  general  mantle-surface  resumes  its  secre- 
tive function  (or  the  latter  becomes  active)  somewhat 
later,  after  the  formation  of  a  definite  varix,  or  thick- 
ened margin  ;  indicating  a  resting  stage  in  the  animal's 
career.  It  is  probable  also  that  during  rapid  growth 
there  is  less  compression  of  the  tissues  than  during  the 
resting-stages.  The  external  sculpture  and  some  of 
the  modifications  of  the  aperture  are  connected  with 
the  functions  of  the  extreme  edge  of  the  mantle ;  those 
we  are  at  present  considering  relate  more  especially  to 
the  function  of  its  general  surface  by  which  the  layer 
which  lines  the  whorls,  the  pillar,  plaits,  and  lirae  are 
solely  secreted  and  deposited. 

"  In  species  with  the  abductor  attached  to  the  pillar 
near  the  aperture,  the  wrinkles  would  be  fewer,  and 
their  action,  if  any,  confined  to  the  vicinity  of  the  mar- 
gin of  the  aperture.  The  deeper  the  attachment,  the 
greater  will  be  the  compression  of  the  secreting  sur- 
face and  the  distance  over  which  it  is  constantly 
dragged  back  and  forth,  and  the  consequent  length  of 
the  ridges  of  shelly  matter  deposited.  If  the  inner  or 
mantle-cone  had  the  whole  cavity  to  itself,  it  is  evident 
that  it  could  and  would  infold  itself  in  a  manner  which 
might  not  appress  its  folds  against  the  inner  surface 
of  the  rigid  outer  or  shell-cone.  But  there  the  mass 
of  the  solid  and  elastic  foot  and  external  body  comes 


KINETOGENESIS. 


259 


into  play,  and  by  its  withdrawal  inward  forces  the 
wrinkled  mantle-cone  against  the  shell.  The  mantle 
is  thus  confined  between  a  rigid  outer  and  an  elastic 
inner  surface,  with  the  result  that  it  cannot  recoil  from 
the  former  and  that  a  certain  uniformity  of  size  and 
direction  is  imposed  upon  the 
wrinkles,  except  where  the  re- 
cess of  the  canal  allows  them  to 
become  more  emphatic,  or  to  a 
less  degree  the  posterior  angle 
permits  a  slight  expansion.  The 
mechanical  principles  involved 
may  be  readily  illustrated  by  the 
experiment  of  pulling  a  hand- 
kerchief through  the  neck  of  a 
bottle,  or  funnel,  followed  by  a 
cork  in  the  center.  Of  course, 
the  more  nearly  the  apparatus 
conforms  to  the  form  and  twist 
of  a  spiral  shell,  the  more  nearly 
the  results  will  approximate 
those  of  nature.  It  is  difficult, 
however,  to  find  any  artificial 
tissue  which  will  correspond  in 
elasticity,  or  capacity  for  partial 
self-contraction,  to  the  living  tis- 
sues concerned  in  nature.  Hence, 
an  exact  conformity  is  not  to  be 
expected,  though  the  mechanical 
principles  may  be  reasonably  well  illustrated. 

"A  comparison  of  specimens  will  show  that  the 
results  exhibited  agree  with  marvellous  precision  with 
the  results  called  for  by  the  preceding  hypothesis, 
based  on  the  dynamical  status  of  the  bodies  concerned, 


Fig.  tfl.—Mitra  lineolata 
Heilprin,  the  body- whorl 
opened,  showing  the  pli- 
cations of  the  columella. 
From  Dall. 


260    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

their  motions  and  secretions.  The  agreement  is  so 
complete  as  to  amount  to  a  demonstration,  though  in 
certain  cases  there  may  be  complications  which  need 
additional  explanation. 

"A  point  which  may- be  noted  in  regard  to  the  Vo- 
lutidae,  to  which  my  attention  was  called  by  Mr.  Pils- 
bry,  is  that  in  this  group  the  mantle  is  greatly  ex- 
tended, and  there  would  be  more  of  it  to  be  wrinkled 
than  in  such  forms  as  Buccinum,  etc.  It  may  be  added 
that  the  forms  in  which  we  note  the 
beginning  of  plaits  for  this  family, 
many  of  them,  such  as  Liopeplum 
and  Volutomorpha,  had  the  mantle 
so  extended  as  to  deposit  a  coat  of 
enamel  over  the  whole  shell,  as  in 
the  modern  Cypraea,  so  that  here  we 
have  an  additional  reason  why  plica- 
tion should  be  emphasized  in  this 
group. 

"Of  course,  as  before  noted,  the 
Fie.  &.-Sifihocypr«a   mechanical  principles  are  the  same 

prooletnatzca   Heilprin ; 

body -whorl     opened,   in    any    group    of     gastropods,     but 

showing  plications  of  among  those  -  which  the  wrinkling 
lips.  From  Dall. 

is  confined  to  the  region  of  the  aper- 
ture, or  those  shells  which  are  lirate  or  dentate,  as 
opposed  to  plicate,  several  other  principles  come  into 
play  which  may  be  briefly  referred  to  in  passing.  In 
the  first  place,  those  species  which  have  a  very  ex- 
tended mantle,  with  hardly  an  exception  have  a  lirate 
aperture  (Oliva,  Olivella,  Cypraea,  Trivia,  etc.).  With 
species  in  which  there  is  a  widely  expanded  mantle 
and  yet  no  lirations,  it  will  usually  be  found  that  the 
mantle  is  not  entirely  withdrawn  into  the  shell  in  such 
forms,  or  is  permanently  external  to  the  shell  (many 


KINETO&ENESIS.  261 

Opisthobranchs,  Marseniidae,  Sigaretus,  Harpa,  etc.). 
In  a  group  like  the  Cypraeidae,  where  nearly  all  the 
species  are  lirate  on  both  lips,  there  are  a  few  which 
want  these  lirae,  and  these  are  species  which  have  a 
wider  aperture  in  the  adult  than  most  of  the  genus, 
and  in  which  we  should  expect  the  wrinkles  to  be  less 
emphatic." 

b.  Mechanical  Origin  of  Characters  in  the  Lamelli- 

branchs  (Pelecypoda). 

Dr.  Robert  T.  Jackson  has  pointed  out1  the  history 
of  the  characters  of  the  retractor  muscle  and  some  of 
those  of  the  list,  of  bivalve  Mollusca.  I  take  the  fol- 
lowing abstract  of  his  conclusions:  "In  the  develop- 
ment of  pelecypods  we  find  in  a  late  embryonic  stage 
(the  phylembryonic)  that  the  shell  has  a  straight  hinge- 
line.  This  is  characteristic  of  Ostrea  (Fig.  59),  Car- 
dium,  Anodonta,  and  so  many  widely  separated  genera 
that  it  apparently  represents  a  primitive  ancestral  con- 
dition common  to  the  whole  class.  Embryology  shows 
that  the  bivalve  shell  doubtless  arose  from  the  split- 
ting on  the  median  line  of  a  primitive  univalvular  an- 
cestor. If  that  ancestor  had  a  saddle-shaped2  or  a 
cup-shaped3  shell,  as  is  probable,  the  first  result  of  the 
introduction  of  a  hinge  in  the  median  line  would  have 
been  to  straighten  the  shell  on  the  hinge-line.  This 
is  a  simple  problem  in  mechanics,  for  if  one  tries  to 
break  by  flexion  a  piece  of  metal  which  is  saddle- 
shaped  or  cup-shaped,  it  will  tend  to  form  a  straight 
line  on  the  axis  of  flexion.  A  parallel  case  is  seen 
in  the  development  of  a  bivalve  shell  in  ancient  crus- 

\Memoirs  of  the  Boston  Society  of  Natural  History,  Vol.  IV.,  No.  8,  p.  277 
July,  1890;  American  Naturalist,  1891,  p.  n. 
2  Characteristic  of  young  Dentalium. 
3Characteristic  of  the  extreme  young  of  cephaious  molUibka. 


262    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

taceans.  The  ancient  Ostracoda,  Leperditia,  Aristo- 
zoe,  etc.,  have  a  straight  hinge-line  and  subcircular 
valves,  which  are  united  dorsally  by  a  ligament.  The 
resulting  form  of  the  early  condition  of  the  bivalvular 
shell  in  these  two  distinct  classes  is  so  strikingly  simi- 
lar, that  it  lends  weight  to  our  supposition  that  the  form 
is  induced  by  the  mechanical  conditions  of  the  case. 

"  I  think  that  the  adductor  muscles  which  close  the 
valves  may  also  be  demonstrated  to  be  the  necessary 
consequence  of  the  bivalvular  condition.  In  the  phyl- 

embryo  stage  (Fig.  59)  the 
valves  are  closed  by  a  single 
adductor  muscle,  which  is  the 
simplest  condition  mechan- 
ically possible  to  effect  the 
desired  end.1  This  muscle 
does  not  seem  homologous 
with  any  muscle  in  other 
classes  of  mollusks,  and  is 
probably  developed  from  the 

Fig-  y).—Ostrea  edulis,  embryo; 

a  ad,   anterior   adductor    muscle;  mantle    mUSCleS    as    a    COnS6- 

m,  mouth;  a,  anus ;  z/,  velum;  h,  quence  of  the  Conditions  of 
hinge  of  shell.  (After  Huxley.)  .  ... 

the  case.     In  support  of  this 

view,  bivalvular  crustaceans  may  again  be  cited.  They 
have  an  analogous  adductor  muscle,  developed,  of 
course,  on  an  entirely  different  line  of  descent,  but  under 
closely  similar  mechanical  conditions.  At  the  completed 
prodissoconch  stage  in  all  pelecypods,  as  far  as  known, 
there  are  two  adductor  muscles,  a  second  one  having 
developed  in  the  posterior  portion  of  the  body.  In 
later  life  the  anterior,  the  posterior,  or  both  adductors 


iThis  early  adductor  appears  in  the  same  position  in  many  genera,  and  is 
apparently  characteristic  of  the  class.  It  is  the  anterior  of  the  two  adductors 
found  in  the  later  stages ;  but  it  may  be  retained  or  lost  in  the  adult. 


KINE  TO  GENESIS.  263 

may  be  retained,  reduced,  or  lost,  according  as  the 
persistence  or  changes  in  correlated  anatomical  fea- 
tures retain  in  use  or  bring  into  disuse  the  muscles  in 
question. 

"Let  us  look  at  examples  of  the  retention  or  loss  of 
the  adductors.  In  typical  dimyarian  pelecypods,  as 
in  Mya  (Fig.  60)  or  Venus,  the  adductors  lie  toward 
either  end  of  the  longer  axis  of  the  shell.  As  the  hinge 
occupies  a  position  on  the  borders  of  the  shell  about 
midway  between  the  adductors,  both  muscles  are  nearly 
or  quite  in  a  position  to  be  equally  functional  in  clos- 


Fig.  60. — Mya  arenaria.  Lettering:  ap  ax,  antero- posterior  axis;  hax?. 
hinge  axis;  a  ad,  anterior,  and  pad,  posterior  adductor  muscle;  m.  mouth; 
//,  palps  ;  a,  anus  ;  g,  gills  ;  pd,  pedal  muscle  ;  f,  foot ;  b,  byssus  ;  A,  heart. 

ing  the  valves.  As  a  result,  both  muscles  are  of  about 
the  same  size.  The  condition  described  is  that  existent 
in  the  completed  prodissoconch  stage  in  all  pelecy- 
pods, as  far  as  known.  In  later  life,  however,  a  revo- 
lution of  the  axes  of  the  soft  parts  may  take  place,  so 
that  the  antero-posterior  axis  (represented  by  a  line 
drawn  through  the  mouth  and  middle  of  the  posterior 
adductor  muscle),  instead  of  being  parallel  to  the 
hinge-axis  (the  axis  of  motion  of  the  valves)  as  in 
dimyarians,  may  present  a  greater  or  less  degree  of 
divergence  from  the  parallel.  In  progressive  series, 


264    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


as  in  Modiola  (Fig.  61),  Perna,  etc.,  as  the  adductor 
muscle  is  brought  nearer  and  nearer  to  the  hinge-line, 


Fig.  61. — Modiola  plicatula.     Lettering  same  as  in  Fig.  60. 

where  its  mechanical  action  is  less   and  less  effectual 
in  closing  the  valves,  we  find  that  it  is  more  and  more 

reduced  until  it  finally  dis- 
appears, from  disuse  and 
atrophy,  as  in  Ostrea  (Fig. 
62),  and  Pecten.  Con- 
versely, the  posterior  ad- 
ductor in  the  same  series  in 
the  revolution  of  the  axes  is 
pushed  farther  and  farther 
from  the  hinge -line  and 
nearer  to  the  central  plane 
of  the  valves,  where  its  me- 
chanical action  is  most  ef- 
fectual in  closing  the  valves. 
With  its  increase  in  func- 
tional activity  the  muscle 
increases  in  size.  The  revolved  position  of  the  axes, 
and  the  consequent  reduction  or  loss  of  the  anterior 
adductor  and  increase  of  the  posterior  adductor,  is 


Fig.  62. — Ostrea  virginiana.   Let- 
tering same  as  in  Fig.  60. 


KINETOGENESIS.  265 

found  in  many  widely  separated  genera  of  pelecypods, 
as  Ostrea,  Mulleria,  and  Tridacna ;  thus  proving  the 
development  of  the  same  features  on  different  lines  of 
descent.1  In  Aspergillum  the  two  valves  have  con- 
cresced  so  as  to  form  a  truly  univalvular,  tubular  shell, 
so  that  the  adductors  would  evidently  be  f  unctionless  if 
existent.  The  posterior  adductor  has  disappeared  and 
the  anterior  is  reduced  to  a  few  disconnected  shreds 
(Fisher),  though  evidently  existent  in  the  young,  as 
attested  by  the  form  of  the  shell  in  the  nepionic  stage. 

"  Ordinarily  there  are  two  posterior  retractor- mus- 
cles of  the  foot  in  pelecypods,  one  situated  on  either  side. 
In  adult  Pecten  either  the  left  retractor  alone  exists, 
or  both  retractors  are  wanting  (the  left  doubtless  al- 
ways exists  in  the  young).  In  studies  of  young  Pecten 
ir radians,  I  found  that  the  animal  always  crawled 
while  lying  on  the  right  side,  with  the  foot  extended 
through  the  notch  in  the  lower  valve  and  pressed 
against  the  surface  of  support.  It  is  evident  that  while 
crawling  in  this  position  the  left  retractor  is  in  the 
plane  of  traction,  and  it  is  retained  ;  on  the  other  hand, 
the  right  retractor  would  not  be  in  the  plane  of  trac- 
tion, and  it  has  disappeared  through  disuse  and  atro- 
phy.2 A  similar  disappearance  of  the  right  retractors 
of  the  foot  is  seen  in  Anomia  glabra,  and  is  explained 
on  similar  bases  of  argument. 

< '  In  My  a  arenaria  we  find  a  highly  elongated  siphon. 
In  the  young  the  siphon  hardly  extends  beyond  the 
borders  of  the  valves,  and  then  the  animal  lives  at  or 

IDr.  B.  Sharp  and  I  published  almost  simultaneously  closely  similar 
views  on  the  mechanical  aspect  of  the  relative  size  of  the  adductors.  See 
Proceeds.  Phila.  Acad.^  1888,  p.  122,  and  Proceeds.  Boston  Soc.  Nat.  Hist.,  Vol. 
XXIII.,  1888,  p.  538. 

2  Both  retractors  doubtless  exist  in  the  prodissoconch  stage  of  Pecten  and 
allies. 


266    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

close  to  the  surface.  In  progressive  growth,  as  the 
animal  burrows  deeper,  the  siphon  elongates,  until  it 
attains  a  length  many  times  the  total  length  of  the 
valves.  The  ontogeny  of  the  individual  and  the  pale- 
ontology of  the  family  both  show  that  Mya  came  from 
a  form  with  a  very  abbreviated  siphon,  and  it  seems 
evident  that  the  long  siphon  of  this  genus  was  brought 
about  by  the  effort  to  reach  the  surface,  induced  by  the 
habit  of  deep  burial. 

"  The  tendency  to  equalize  the  form  of  growth  in  a 
horizontal  plane  in  relation  to  the  force  of  gravity  act- 
ing in  a  perpendicular  plane,  or  the  geomalic  tendency 
of  Professor  Hyatt,1  is  seen  markedly  in  pelecypods. 
In  forms  which  crawl  on  the  free  borders  of  the  valves 
the  right  and  left  growth  in  relation  to  the  perpendic- 
ular is  obvious,  and  agrees  with  the  right  and  left  sides 
of  the  animal.  In  Pecten  the  animal  at  rest  lies  on 
the  right  valve,  and  swims  or  flies  with  the  right  valve 
lowermost.  Here  equalization  to  the  right  and  left  of  the 
perpendicular  line  passing  through  the  center  of  grav- 
ity is  very  marked  (especially  in  the  Vola  division  of 
the  group)  ;  but  the  induced  right  and  left  aspect  cor- 
responds to  the  dorsal  and  ventral  sides  of  the  animal, 
— not  the  right  and  left  sides,  as  in  the  former  case. 
Lima,  a  near  ally  of  Pecten,  swims  with  the  edges  of 
the  valves  perpendicular.  In  this  case  the  geomalic 
growth  corresponds  to  the  right  and  left  sides  of  the 
animal. 

"The  oyster  has  a  deep  or  spoon-shaped  attached 
valve  and  a  flat  or  flatter  free  valve.  This  form,  or  a 
modification  of  it,  we  find  to  be  characteristic  of  all 


1"  Transformations  of  Planorbis  at  Steinheim,  with  Remarks  on  the  Ef- 
fects of  Gravity  Upon  the  Forms  of  Shells  and  Animals."  Proceeds.  A.  A.  A. 
S.,  Vol.  XXIX.,  1880. 


KINETOGENESIS,  267 

• 

pelecypods  which  are  attached  to  a  foreign  object  of 
support  by  the  cementation  of  one  valve.  All  are 
highly  modified,  and  are  strikingly  different  from  the 
normal  form  seen  in  locomotive  types  of  the  group. 
The  oyster  may  be  taken  as  the  type  of  the  form 
adopted  by  attached  pelecypods.  The  two  valves  are 
unequal,  the  attached  valve  being  concave,  the  free 
valve  flat ;  but  they  are  not  only  unequal,  they  are 
often  very  dissimilar, — as  different  as  if  they  belonged 
to  a  distinct  species  in  what  would  be  considered  typ- 
ical forms.  This  is  remarkable  as  a  case  of  acquired 
and  inherited  characteristics  finding  very  different  ex- 
pression in  the  two  valves  of  a  group  belonging  to  a 
class  typically  equivalvular.  The  attached  valve  is 
the  most  highly  modified,  and  the  free  valve  is  least 
modified,  retaining  more  fully  ancestral  characters. 
Therefore,  it  is  to  the  free  young  before  fixation  takes 
place  and  to  the  free,  least-modified  valve  that  we 
must  turn  in  tracing  genetic  relations  of  attached 
groups.  Another  characteristic  of  attached  pelecy- 
pods is  camerated  structure,  which  is  most  frequent 
and  extensive  in  the  thick  attached  valve.  The  form 
as  above  described  is  characteristic  of  the  Ostreidae, 
Hinnites,  Spondylus,  and  Plicatula,  Dimya,  Pernos- 
trea,  Aetheria,  and  Mulleria;  and  Chama  and  its  near 
allies.  These  various  genera,  though  ostreiform  in 
the  adult,  are  equivalvular  and  of  totally  distinct  form 
in  the  free  young.  The  several  types  cited  are  from 
widely  separated  families  of  pelecypods,  yet  all,  under 
the  same  given  conditions,  adopt  a  closely  similar 
form,  which  is  strong  proof  that  common  forces  acting 
on  all  alike  have  induced  the  resulting  form.  What 
the  forces  are  that  have  induced  this  form  it  is  not 
easy  to  see  from  the  study  of  this  form  alone ;  but  the 


268    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

ostrean  form  is  the  base  of  a  series,  from  the  summit 
of  which  we  get  a  clearer  view." 

c.   Mechanical   Origin   of  the  Impressed  Zone  in  Cepha- 
lopoda. 

Prof.  Alpheus  Hyatt  has  shown  that  the  groove  on 
the  dorsum  or  inside  of  each  coil  of  the  Cephalopoda 
is  due  to  the  pressure  exercised  by  contact  with  the 
ventral  side  of  the  coil  within  it.  He  has  shown  that 
this  groove  persists  in  cases  where  the  shell  in  the 
course  of  evolution  has  become  more  or  less  unwound, 
and  he  regards  this  as  an  example  of  the  inheritance 
of  a  mechanically  acquired  character.  This  subject  is 
presented  in  greater  detail  in  the  part  of  this  book  de- 
voted to  heredity. 

3.    KINETOGENESIS    IN    VERMES    AND  ARTHROPODA. 

It  is  believed  with  good  reason  that  the  Arthropoda 
have  descended  from  some  of  the  forms  included  in 
the  branch  Vermes,  and  perhaps  Peripatus  furnishes 
the  nearest  living  approach  to  that  type.  The  ances- 
tor, whatever  it  may  have  been,  developed  limbs  from 
processes  of  the  body-wall,  and  used  them  to  aid  in 
progression.  Peripatus  has  soft  flexible  limbs,  and  a 
non-chitinous  integument  generally.  With  the  begin- 
ning of  induration  of  the  integument,  segmentation 
would  immediately  appear,  for  the  movements  of  the 
body  and  limbs  would  interrupt  the  deposit  at  such 
points  as  would  experience  the  greatest  flexure.  The 
muscular  system  would  initiate  the  process,  since  flexure 
depends  on  its  contractions,  and  its  presence  in  ani- 
mals prior  to  the  induration  of  the  integuments  in  the 
order  of  phylogeny,  furnishes  the  condition  required. 
It  is  a  matter  of  detail  how  the  diverse  segmentations 


KINETOGENESIS.  269 

of  existing  forms  were  produced.  We  can  believe, 
however,  that,  as  in  Vertebrata,  there  has  been  a 
gradual  elimination  of  less  important  segments  of  the 
limbs,  until  the  highest  mechanical  efficiency  was  at- 
tained. We  well  know  how  the  segments  of  the  head 
and  body  have  been  modified  by  fusion,  etc. 

Prof.  B.  L.  Sharp  has  shown  the  mechanical  con- 
ditions of  segmentation  in  Arthropoda  as  follows:1 

"It  occurred  to  me  that  if  the  theory  [of  kineto- 
genesis]  had  a  general  application,  some  additional 
proofs  could  be  shown  to  exist  among  the  inverte- 
brates, where  we  have  the  action  of  muscular  force 
upon  hard  and  resisting  parts  of  the  skeleton.  Those 
which  present  the  best  study  for  this  purpose  appear 
to  be  the  crustaceans,  where  we  find  an  immense  va- 
riety of  articulations  in  the  body  and  in  the  limbs; 
highly  complicated  locked  joints,  others  allowing  mo- 
tion in  but  one  plane,  as  well  as  loose  joints,  where 
the  hard  parts  scarcely  come  in  contact  with  one 
another,  and  cases  of  degeneration  of  the  hard  parts, 
leading  to  total  disappearance  of  a  previously  existing 
joint. 

"In  the  Anneiides,  from  which,  there  is  no  doubt, 
the  arthropod  branch  sprang,  we  find  no  deposit  of 
inorganic  salts  in  the  epidermis.  The  outer  layer  of 
the  body  is  generally  of  a  horn-like  character,  adher- 
ing closely  to  the  secretive  cells  of  the  epidermis,  very 
flexible,  and  thrown  into  folds  by  the  vermicular  mo- 
tion of  its  possessor.  In  the  leeches  the  body  consists 
of  a  flexible  cylinder,  made  up  of  two  sets  of  muscles, 
an  outer  longitudinal  cylinder  and  an  inner  cylinder  of 
circular  fibers*  the  contraction  of  which  causes  the 
animal  to  increase  in  length,  while  shortening  is  ef- 

1  American  Naturalist,  1893,  p.  89. 


270    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


fected  by  the  contraction  of  the  longitudinal  layer. 
The  external  surface  of  the  medicinal  leech,  for  exam- 
ple, is  thrown  into  a  regular  series  of  very  fine  folds, 
extending  across  the  longitudinal  axis  of  the  body. 
These  folds  do  not  correspond  in  numbers  to  the  so- 
mites of  the  body,  which  are  not  indicated  externally, 
five,  six,  or  more  of  them  belonging  to  one  somite. 
When  the  animal  shortens  its 
length,  these  folds  are  deepened 
and  the  segments  thrown  closely  to- 
gether ;  when  extension  takes  place, 
the  folds  are  flattened,  spread  open, 
although  not  wholly  disappearing, 
as  they  are  a  fixed  quantity,  so  to 
speak.  I  believe  these  folds  are 
due  to  mechanical  action  ;  by  the 
disposition  of  the  different  fibers  of 
the  longitudinal  series,  in  being  in- 
serted in  a  series  of  planes  bounded 
by  the  valleys  between  the  folds, 
this  being  aided  by  some  of  the 
circular  fibers  which  pass  through 
Fig.  63.-Diagraminatic  the  longitudinal  sheath,  and  find 

representation  of  the  seg-  . 

ments  of  the  leech,  show-  their  attachment  to  the  bases  of  the 

ing  the  folds,  valleys,  and    valleys, 
muscular  fibers. 

'  Starting  from   this  point,  and 

supposing  the  regularity  of  the  folds  to  have  become 
established  from  preexisting  folds  by  the  regularity  and 
stress  of  muscular  action,  we  can  conceive  that  when 
deposits  of  calcareous  matter  took  place,  rings  simi- 
larly formed  by  a  folding  of  a  soft  skin  would  receive 
that  deposit  at  the  most  prominent  portion  of  this  fold, 
the  convex  face,  and  not  in  the  protected  valleys,  as 
there  would  be  more  friction  or  pressure  from  external 


KINE  TO  GENE  SIS. 


271 


causes,  and  no  deposits  would  take  place  in  the  val- 
leys themselves,  because  they  would  not  be  subject 
to  external  friction,  and  their  continual  flexion  would 
prevent  any  such  deposits.  Should  such  a  deposit 
take  place  in  the  valleys,  there  would  be  a  stiffening 
of  the  whole  surface,  which  would  defeat  motion.  In 
fact,  in  the  leech  the  cuticle  is  already  much  thicker 
on  the  crests  of  the  folds  than  in  the  valleys. 

* '  In  the  more  primitive  Crus- 
tacea, we  find  the  animal  made  up 
of  rings  extending  over  the  whole 
length  of  the  body,  similar  to  the 
rings  of  the  leech,  save  that  there 
is  but  one  ring  to  one  somite,  and 
instead  of  a  perpendicular  valley 
between  the  folds,  this  valley  has 
an  inward  and  a  forward  direction, 
allowing  the  anterior  edge  of  a 
caudad  ring  to  fit  into  the  posterior 
edge  of  a  cephalad  ring. 

.  "In  the  higher  Crustacea,  sev- 
eral of  the  anterior  rings  have  co- 
alesced and  form  a  solid  shield 
which  is  known  as  the  carapace. 
This  has  no  doubt  arisen  by  the 
lessening  of  the  action  between  the 
anterior  rings  when  the  posterior  portion  of  the  body 
became  the  moie  active  propelling  organ.  As  the  ac- 
tion ceased  forward  the  valleys  came  to  rest,  and  be- 
came exposed  to  friction  and  pressure,  and  conse- 
quently a  deposit  of  calcareous  matter  took  place  pro- 
ducing the  stiffening  above  hinted  at. 

"The  formation  of  jointed  appendages  from  para- 
podic  paddles  of  the  annelids  can  be  followed  out  in 


Fig.  64.  —  Diagram- 
matic representation  of 
the  rings  of  a  primitive 
crustacean, showing  the 
action  of  the  muscles. 


272    PRIMAKV  FACTORS  OF  ORGANIC  EVOLUTION, 

the  same  manner,  since  the  manner  of  mutual  relation 
of  the  segments  is  the  same  as  in  the  case  of  the  body- 
segments. 

"  It  has  been  stated  that  in  the  leech  the  folds  do  not 
correspond  in  number  to  the  somites  of  the  body,  while 
they  do  in  the  Crustacea.  All  annelids  do  not  move 
by  means  of  a  muscular  system  built  upon  the  plan 
found  in  the  leech.  In  many  the  circular  layer  has  to 
a  large  extent  disappeared,  for  the  longitudino-circular 
plan  is  undoubtedly  ante-annelidan.  The  movement 
of  the  free  medusoid  forms,  and  of  the  Ctenophora,  is 
the  result  of  a  modified  arrangement  of  this  plan. 

"With  the  disappearance  of  the  circular  layer,  we 
find  a  peculiar  modification  of  the  longitudinal  layer. 
This  layer  becomes  broken  up  and  the  fibers  act  in 
moving  the  setae,  which  answer  to  limbs.  In  a  seg- 
ment of  a  setiferous  annelid,  we  may  observe  that  the 
longitudinal  muscles  of  the  somite  in  section  at  the  po- 
sition of  the  seta  are  arranged  like  the  letter  'V  in 
the  fork  of  which  the  seta  lies,  the  fibers  to  the  left 
(anterior)  pull  the  seta  externally  backward,  those  on 
the  right  (posterior)  pull  the  seta  forward.  The  in- 
troduction of  the  setae,  the  origin  of  which  I  do  not 
here  attempt  to  explain,  has  no  doubt  been,  together 
with  the  establishment  of  the  external  segmentation,  a 
strong  factor  in  causing  the  breaking  up  of  the  muscu- 
lar tube  into  sections  (myotomes),  which  by  use  and 
consequent  increase  have  extended  each  arm  of  the 
'V  into  the  segment  on  each  side,  while  the  insertion 
of  the  end  of  the  seta  has  caused  a  break  in  the  muscle 
by  the  formation  of  an  aponurosis.  This  gives  us  the 
peculiar  disposition  of  a  myotome  to  extend  across  the 
union  of  two  somites. 

"If  we  examine  the  segments  of  the  so-called  ab- 


KINETOGENESIS.  273 

domen  of  the  macrurous  Crustacea,  as  the  lobster,  we 
will  find  that  the  anterior  face  of  one  abdominal  ring 
is  pulled  into  the  posterior  orifice  of  the  ring  lying  an- 
terior to  it,  forming  a  kind  of  tubular  ball  and  socket- 
joint,  but  with  a  flexible  part  of  the  integument  with 
no  calcareous  deposit,  folded  upon  itself,  and  acting 
physiologically  as  a  tubular  ligamentum  teres.  On  ex- 
amining the  different  joints,  we  will  find  that  com- 
mencing at  a  fixed  point,  as  at  the  base  of  the  thorax, 
the  movable  ring  of  the  first  abdominal  somite  is  pulled 
into  the  fixed  part.  Then  the  first  abdominal  somite  be- 
comes the  fixed  point  for  the  movable  ring  posterior  to 
it,  and  so  on,  so  that  we  find  that  as  the  rings  proceed 
away  from  the  thorax,  each  is  pulled  into  the  opening 
of  the  one  in  advance.  This  is  true  of  all  those  forms 
where  the  abdomen  is  well  formed,  strong,  and  an  ac- 
tive organ  in  the  economy  of  the  animal ;  when  this 
organ,  the  abdomen,  ceases  to  be  an  active  organ  of 
motion,  as  in  the  burrowing  forms,  as  in  Callianassa, 
Gebia,  some  of  the  Squillidae,  etc.,  or  where  it  is  folded 
upon  the  sternum  of  the  thoracic  region,  the  muscles 
becoming  weaker  through  disuse,  the  rings  are  not 
subject  to  the  powerful  muscular  strain,  and  they  as  a 
rule  overlap  but  little,  if  at  all,  but  lie  so  that  the  edge 
of  one  ring  rests  upon  the  edge  of  another.  In  those 
forms  where  degeneration  of  the  abdomen  has  pro- 
ceeded so  far  as  not  to  have  even  the  usual  deposit  of 
calcareous  matter,  as  in  the  hermit  crabs,  there  are 
simply  indications  of  rings  on  the  abdomen,  and  this 
organ  is  but  little  more  than  a  fleshy  sac  containing 
some  of  the  viscera,  and  supplied  with  a  few  muscles 
which  act  together,  with  the  form  of  the  organ,  to  keep 
the  abdomen  curled  so  that  it  may  hold  as  a  hook,  the 


274    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


animal  within  the  molluscan   shell  which  it  habitually 
inhabits. 

"When  the  limbs  are  examined,  the  same  rule  will 
be  found  to  hold  good,  viz. :  that  the  movable  part  is 
pulled  into  the  fixed  part.  A  modification  of  this  is 
well  illustrated  in  the  evolution  of  the  large  chelae.  In 
some  forms,  take  for  example  Ibacus,  the  first  pair, 
and  in  fact  all  of  the  thoracic  limbs  end  in  a  sharp- 
pointed  segment,  there  being  not  the  slightest  sugges- 
tion of  a  chela.  In  Crangon,  on  the  other  hand,  the 

terminal  segment  is  pulled 
against  the  broad  face  of  the 
penultimate  one  thus  making 
a  shift  for  a  chela.  In  the 
Stomatopoda  this  step  has 
been  developed,  for  the  last 
segment  can  be  drawn  against 
the  whole  length  of  the  pen- 
ultimate one  (which  is  some- 
times grooved  to  protect  the 
points  of  the  spines  of  the 
latter)  and  forms  with  it  a 
very  effective  grasping  or- 
gan. The  continual  use  of 
the  terminal  segment,  the 
increase  of  the  muscular  power  will  tend  to  draw  this 
terminal  segment  backward  (into)  on  the  penultimate 
which  enlarges  with  the  increase  of  bulk  of  muscle,  so 
that  a  well-developed  chela,  as  in  the  lobster  is  found, 
where  the  ultimate  segment  is  pulled  backward  to 
about  the  middle  of  the  penultimate  segment." 


Fig.  65.— Diagrams  of,  a,  hand 
of  a  form  of  Crangon  ;  b,  hand  of  a 
form  of  Astacus. 


KINE  TOGENESIS.  275 


4.  KINETOGENESIS  IN  THE  VERTEBRATA. 

I  have  already  adduced  the  evidence  in  support  of 
the  doctrine  that  the  structures  of  the  hard  parts  of 
invertebrates  have  been  produced  by  muscular  move- 
ments. In  turning  to  the  Vertebrata  we  shall  find  that 
the  evidence  indicating  that  the  details  of  their  hard 
parts  have  had  a  similar  origin,  is  quite  convincing. 
This  branch  of  the  animal  kingdom  presents  two  dis- 
tinct advantages  for  this  study.  First,  we  have  a  more 
complete  paleontologic  series  than  in  any  other.  Sec- 
ond, we  have  the  best  opportunity  for  observation  and 
experiment  on  their  growth  processes,  since  we  our- 
selves, and  our  companions  of  the  domesticated  ani- 
mals, belong  to  this  branch  of  the  animal  kingdom. 

I  shall  show  first,  the  conditions  under  which  ab- 
normal articulations  of  the  skeleton  have  been  formed  ; 
and  then  the  process  involved  in  the  formation  of 
normal  articulations.  I  shall  then  apply  these  facts 
to  the  phylogeny  of  the  Mammalia  as  we  know  it,  and 
then  in  a  more  general  way  to  the  Vertebrata  as  a 
whole. 

i.     KINETOGENESIS  OF  OSSEOUS  TISSUE. 

a.   Abnormal  Articulations. 

Hiitter,  from  whom  I  have  quoted  under  the  head 
of  "  Kinetogenesis  of  Muscle,"  thus  describes  the  effect 
of  abnormal  conditions  of  joints  on  the  articular  sur- 
faces of  the  bones  which  form  them.  He  says:  "We 
have  abundant  opportunity  to  investigate  the  change 
of  condition  which  the  joints  undergo  during  a  year  of 
fixed  muscular  contraction. 

"The  ligaments  and  bursae  undergo  similar  changes 


276    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

to  those  described  for  the  muscles  concerned.  They 
elongate  at  points  where  the  articular  surfaces  are 
spread  apart,  and  correspondingly  shorten  where  the 
flexure  produces  a  folding.  These  changes  proceed 
more  slowly  than  those  of  the  muscles  and  tendons. 
Very  remarkable  are  the  changes  undergone  by  the 
articular  cartilages.  When  a  joint  is  permanently 
flexed,  a  part  of  the  extremity  of  each  bone  is  separated 
from  contact  with  the  other,  and  the  articulation  is 
finally  destroyed  at  this  point,  because  the  cartilage 
begins  to  vanish.  One  must  conclude  that  the  exist- 
ence of  the  articular  cartilages  is  dependent  on  their 
mutual  contact ;  for  dislocated  articular  surfaces  which 
remain  in  contact  with  soft  tissues  only,  lose  their  car- 
tilaginous covering.  .  .  .  Finally  it  is  possible  by  a 
consideration  of  the  etiology  of  the  effects  of  joint  con- 
tractions to  reach  some  hitherto  unnoticed  conclusions 
regarding  the  changes  of  articular  surfaces,  and  bone 
forms.  The  results  of  joint-contraction  are  most  con- 
spicuous when  the  latter  occurs  in  childhood.  During 
maturity,  a  dislocation  which  causes  an  articular  bor- 
der or  prominence  to  rest  abnormally  on  the  opposed 
articular  face  in  the  act  of  walking,  will  be  followed  by 
the  penetration  of  the  former  into  the  latter,  and  a  de- 
formation of  the  articulation  ;  but  the  corresponding 
changes  under  like  conditions  in  the  growing  skeleton 
are  much  more  conspicuous." 

Hutter  thus  describes  the  formation  of  new  artic- 
ular surfaces  as  a  consequence  of  dislocation  of  joints. 
"  If  the  head  of  the  femur  or  humerus  leaves  its  socket, 
and  rests  on  the  side  of  the  ilium  or  the  scapula,  the 
periosteum  of  the  bone  which  receives  the  new  impact 
is  excited  to  active  bone-production,  and  the  result  is 
the  deposit  of  new  osseous  tissue.  The  thin  bones 


KINETOGENESIS.  277 

become  thicker,  not  uniformly,  but  in  correspond- 
ence with  the  periphery  of  the  head  of  the  humerus  or 
femur,  rather  than  with  the  point  of  contact  of  the 
latter.  This  point  is  irritated,  but  the  contact  of  the 
ball  restrains  osseous  deposit.  So  it  occurs  that  grad- 
ually a  new  socket  is  developed,  whose  mechanical 
relations  correspond  exactly  with  those  of  the  articu- 
lating bone.  The  head  also  acquires  a  strictly  spher- 
ical shape,  by  such  contractions  and  atrophies  as  are 
necessary  to  produce  that  result.  Further,  cartilage 
appears  in  the  place  of  the  periosteum  of  the  socket, 
which  functions  like  the  primitive  articular  cartilage. 
It  is  characteristic  of  both  connective  and  periosteal 
tissue  to  develop  cartilage  under  the  stimulus  of  con- 
tinued friction  of  hard  surfaces,  such  as  occurs  in  dis- 
locations and  fractures." 

These  observations  of  Hutter  have  been  confirmed 
by  Henke,  Reyher,  Moll,  and  Lesshaft.  Henke  and 
Reyher  state  that  the  artificial  prevention  of  flexure  of 
articulations  in  young  dogs  renders  them  immobile, 
and  their  restraint  of  flexure  to  one  direction,  results 
in  a  curving  of  the  articular  faces  in  that  direction. 

I  cite  here  two  examples  of  modifications  of  struc- 
ture under  abnormal  conditions  which  imposed  new 
impacts  and  strains  on  the  parts.  I  have  described 
these  cases,  which  are  examples  of  false  elbow-joints 
in  man  and  in  the  horse,  in  the  Proceedings  of  the  Amer- 
ican Philosophical  Society  for  1892. 

In  the  first  case,  that  of  the  human  elbow,  the 
cubitus  was  luxated  posteriorly,  so  that  the  humeral 
condyles  articulate  with  the  ulna  anterior  to  the  coro- 
noid  process.  The  head  of  the  radius  is  in  contact 
with  the  external  epicondyle  on  its  posterior  inferior 
face.  The  results  are  as  follows.  A  new  coronoid 


278    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

process  was  developed  in  front  of  the  abnormal  posi- 
tion of  the  humeral  condyle  to  an  elevation  above  the 
shaft  of  the  ulna  exceeding  that  of  the  normal  coro- 
noid.  Between  it  and  the  normal  coronoid  was  devel- 
oped a  perfectly  functional  cotylus  which  embraces 
the  humeral  condyle  like  the  normal  cotylus.  The 
latter  has  its  articular  surface,  buried  under  osseous 
deposit,  so  as  to  be  no  longer  visible.  The  region  of 
contact  between  the  head  of  the  radius  and  the  external 
epicondyles,  lias  developed  in  the  latter  a  large  artic- 
ular cotylus  which  permits  of  both  rotary  and  ver- 
tical movement  of  the  former.  The  articular  surface 
of  the  humeral  condyles,  except  where  in  articulation 
with  the  ulna,  is  roughened,  and  partially  overgrown 
with  exostoses,  so  as  to  alter  its  form  to  a  great  extent. 
The  opportunity  of  examining  this  specimen  I  owe  to 
Provost  Pepper  of  the  University  of  Pennsylvania,  in 
whose  museum  it  is  preserved. 

In  the  case  of  the  horse's  elbow,  the  luxation  of 
the  cubitus  is  inward,  so  that  the  olecranon  articulates 
with  the  external  epicondylar  surface,  and  the  humeral 
condyles  are  not  adapted  to  the  head  of  the  radius  ; 
their  internal  border  falling  considerably  internal  to 
the  inner  border  of  the  radius.  The  horse  from  which 
this  specimen  was  derived  lived  for  two  years  after  the 
luxation  took  place,  and  became  able  to  use  the  limb 
in  some  degree.  The  effect  on  the  articulation  is  as 
follows. 

A  large  part  of  the  inferior  extremity  of  the  poste- 
rior rib  of  the  shaft  of  the  humerus,  which  is  the  place 
of  insertion  of  the  extern ^  flexor  metacarpi  muscle,  has 
been  removed,  so  as  to  present  a  wedge-shaped  out- 
line with  the  apex  downward.  This  removal  permits 
the  close  articulation  of  the  inner  face  of  the  olecranal 


KINETOGENESIS.  279 

process  with  the  epicondyle,  which  has  developed  a 
considerable  articular  face,  on  which  movement  takes 
place  in  extension  and  flexion.  The  posterior  border 
of  this  face  has  developed  a  ridge  which  borders  the 
facet  behind,  and  retains  the  olecranon  in  place.  Two 
other  facets  are  developed  on  the  humeral  condyles, 
and  two  on  the  head  of  the  radius.  The  most  impor- 
tant of  the  latter  is  a  bevel  of  the  external  part  of  the 
surface  to  the  border,  due  to  the  contact  of  the  ex- 
panded internal  humeral  condyle.  The  articular  face 
of  the  olecranon  is  much  depressed  in  consequence  of 
its  articulation  with  the  external  epicondyle  of  the 
humerus.  Besides  these  new  and  changed  facets,  the 
effect  of  the  luxation  is  seen  in  the  development  of  os- 
seous crests  at  the  points  of  insertion  of  the  articular 
ligaments.  One  of  these  on  the  humerus  has  been  al- 
ready referred  to.  Another  is  concentric  with  and 
posterior  to  the  internal  humeral  facet  of  the  olecranar 
process,  and  serves  as  a  guide  to  the  humeral  crest 
above  described.  A  third  is  an  extensive  osseous  de- 
posit on  the  internal  face  of  the  head  of  the  radius, 
which  partially  builds  an  extension  of  the  head  of  the 
radius,  which  if  completed  would  articulate  with  the 
overhanging  portion  of  the  internal  humeral  condyle. 
A  third  modification  of  normal  structure  is  similar  to 
that  observed  in  the  human  elbow.  It  consists  of  os- 
seous deposit  beneath  the  synovial  bursa  at  points 
where  the  luxation  causes  a  gaping  of  the  surfaces. 
This  occurs  at  the  trochlear  groove  of  the  head  of  the 
radius,  which  is  partially  filled  up  with  exostosis. 

The  preceding  observations  lead  to  the  following 
conclusions  : 

First.  Continued  excessive  friction  removes  osse- 
ous tissue  from  the  points  of  contact  until  complete 


282    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

adaptation  is  accomplished  and  the  friction  is  reduced 
to  a  normal  minimum.  Then  a  normal  articular  sur- 
face is  produced. 

Second.  Where  the  normal  friction  is  wanting, 
and  an  inflammatory  condition  is  maintained  by  a  pull- 
ing stress  on  the  investing  synovial  membrane,  excess 
of  osseous  deposit  is  produced. 

Third.  Stress  on  the  articular  ligaments  and  ten- 
dons stimulates  osseous  deposit  at  their  insertions, 
which  deposit  may  be  continued  into  their  substance. 
This  is  a  pulling  stress. 

These  observations  therefore  show  that  osseous  de- 
posit is  produced  by  different  forms  of  mechanical 
stimulus. 

EXPLANATION  OF  FIGURES  66  AND  67. 

1-5,  Homo  sapiens,  luxated  elbow  joint  (one-half  natural  size) ;  i,  luxated 
elbow  joint,  from  within ;  2,  luxated  elbow  joint,  from  outer  side;  3,  humerus, 
posterior  view  of  distal  region;  4,  humerus,  distal  view;  5,  ulna  and  radius, 
anterior  (superior)  view ;  6-n,  bones  of  abnormal  left  elbow  joint  of  horse 
(one-half  natural  size)  ;  12,  13,  normal  bones  of  elbow  joint  of  horse  (one-half 
natural  size);  6-12,  humerus,  distal  views;  7-13,  cubitus,  proximal  views ;  8, 
humerus,  external  view  of  distal  extremity;  9,  humeral  articulation  of  cubi- 
tus, from  above;  10,  cubitus,  internal  view ;  n,  cubitus,  external  view.  Let- 
tering.— Ht  humerus ;  U,  ulna  ;  R,  radius  ;  C,  coronoid  process  ;  Czt  second 
(abnormal)  coronoid  process ;  O,  olecranon  ;  En,  entepicondyle  ;  EC,  ectepi- 
condyle  ;  Eno,  entepicondylar  exostosis  ;  Eco,  ectepicondylar  exostosis  ;  Co, 
condylar  exostosis ;  Cos,  superior  condylar  exostosis  ;  Cot,  inferior  condylar 
exostosis ;  Hf,  humeral  facet ;  Rf,  radial  facet ;  Uf,  ulnar  facet ;  Op,  olecranar 
process  of  ulna ;  Cp,  coronoid  process  of  ulna;  Og,  olecranar  groove  of  hu- 
merus ;  Tc,  trochlear  crest  of  humerus ;  Tg,  trochlear  groove  of  humerus  ; 
Ehc,  external  humeral  facet  of  coronoid  process ;  Ihc,  internal  humeral  facet 
of  coronoid  process ;  la,  abnormal  facet  for  coronoid  process  of  ulna ;  ib, 
do.  for  internal  roller  of  humerus;  ic,  do.  for  abnormal  facet  of  humerus; 
id,  do.  for  internal  border  of  radius;  le,  do.  for  olecranar  process  of  ulna  ; 
if,  do.  for  trochlear  crest  of  humerus;  2a,  2b,  2c,  exostoses  of  radius  and  ulna 
to  fill  vacuity  between  humerus  and  radius  and  ulna,  ja,  abnormal  crest 
which  serves  as  a  guide  to  the  olecranar  process  of  the  humerus  ;  jb,  abnormal 
crest  which  serves  as  a  guide  to  abnormal  crest  30. ;  jc,  exostosis  extending 
head  of  radius  inwards  to  equalize  its  width  with  inward  luxation  of  humerus ; 
3d,  exostoses  of  external  epicondyle  of  humerus,  to  equalize  its  width  with 
outward  luxation  of  radius;  je,  abnormal  exostosis  of  insertion  of  external 
tfexor  metacarpi  muscle  ;  jf,  3g,  abnormal  crest  at  insertion  of  external  ar- 
ticular ligament  on  olecranar  process  of  ulna. 


KINETOG&NESIS.  283 


b.   Normal  Articulations. 

The  origin  of  condyles  and  their  corresponding 
cotyli  has  been  made  the  subject  of  investigation  by 
several  German  anatomists.  L.  Fick1  expressed  the 
opinion  that  the  concavo-convex  surfaces  were  pro- 
duced by  a  wearing  away  of  the  surface  which  became 
concave,  by  the  free  action  on  it  of  the  surface  which 
became  convex,  the  former  being  fixed,  and  the  latter 
free.  He  found  the  conditions  of  muscular  insertions 
to  correspond  with  the  conditions  of  fixity  and  free- 
dom required  ;  for  the  insertions  are  always  nearer  to 
the  concave  surface  than  to  the  convex  surface.  He 
constructed  plaster  models  of  joints,  and  by  moving 
one  on  the  other  obtained  a  convex  surface  on  the 
moving,  and  a  concave  surface  on  the  fixed  extremi- 
ties. These  observations  were  confirmed  by  Henke,'2 
but  he  very  properly  does  not  regard  the  result  as  due 
to  wearing,  but  to  the  stimulation  of  metabolic  action 
in  the  required  directions.  R.  Fick3  has  confirmed 
these  positions  in  an  extended  memoir,  and  recently 
Dr.  E.  Tornier  has  devoted  a  still  more  thorough  re- 
search to  the  same  subject.4  R.  Fick  applied  his  ob- 
servations to  the  question  of  the  phylogeny  of  the  ar- 
ticulations, but  did  not  see  in  it  proof  of  the  operation 
of  mechanical  causes,  but  ascribed  it  to  "inheritance 
and  natural  selection  "  in  accordance  with  the  mean- 
ingless formula  usual  at  the  time  he  wrote.  W.  Roux,5 
however,  in  reviewing  Fick's  article  saw  in  the  obser- 

1  Ueber  die   Ursachen  der  Knochenformcn ,   Experimental-  Untersuchung, 
1859,  Gottingen,  G.  Wiegand. 

2  Anatomic  und  Mechanik  der  Gelenke,  Leipsic,  1863,  p.  57. 
SArchivfiir  Anatomie  und  Physiologic,  1890,  p.  391. 

4  Archii> filr  Entiuickelungsmechanik,  I.,  1894,  p.  157. 

5  Biologisches  Centralblatt,  1891,  p.  188. 


284    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

vations  of  Fick  proof  of  a  direct  mechanical  cause  of 
the  structure.  I  have  pointed  out  the  phylogeny  of 
the  articulations  in  the  Mammalia  in  various  papers 
from  1877!  to  i88g,2  and  in  1881  I  advanced  the  view 
that  their  successive  evolution  was  due  to  impacts  and 
strains  {American  Naturalist,  July,  1881  ;  Origin  of  the 
Fittest,  p.  373).  The  opinion  of  Roux  entirely  sup- 
ports my  position,  and  it  is  further  established  by  the 
elaborate  memoir  of  Tornier  just  cited.  This  author 
adopts  the  view  that  bone- development  is  controlled 
by  Druck  und  Zug  or  impact  and  strain,  and  he  adds 
some  important  considerations  to  those  previously  ad- 
vanced. Reasserts  that  "in  all  existing  Vertebrata 
true  bones  may  appear  as  secondary  structures,  since 
all  of  these  animals  possess  bands  and  threads  of  con- 
nective tissue  which  possess  the  latent  capacity  to  be 
changed  wholly  or  in  part  into  cartilage. "  Thus  is 
accounted  for  the  development  of  sesamoid  bones  in 
tendons,  in  which  category  is  included  the  patella. 
Tornier  also  shows  that  the  concave  articular  face 
(cotylus)  is  that  to  which  the  flexor  and  extensor  mus- 
cular insertions  are  nearest,  while  the  convex  face 
(condyle)  is  the  one  most  remote  from  the  muscular 
insertions. 

It  must  be  observed  that  Tornier  adopts  the  lan- 
guage of  the  American  Neo-Lamarckians  in  using  the 
expression  "impact  and  strain."  Impact  and  strain 
are  different  modes  of  motion.  "Impact"  implies 
pressure,  while  "strain  "  implies  a  pulling  stress,  either 
direct  or  torsional.  It  is  therefore  alleged  by  Tornier, 
as  it  has  been  by  myself,  that  opposite  modes  of  mo- 

\Report  U.  S.  Geol.   Survey   W.  of  jooth   Meridian,  1875,  Vol.  IV.,  p.  277- 
279.     Proceeds.  Amer.  Philosoph.  Soc.,  1884,  p.  44. 
2  Amer.  Journal  Morphology,  1889,  p.  163. 


KINETOGENESIS.  285 

tion  may  produce  metabolic  changes  in  osseous  tissue. 
For  this  reason  it  is  possible  to  account  for  the  length- 
ening of  the  limb-bones  in  heavy  animals,  as  an  effect 
of  impact,  while  the  astragalus  of  bats  may  have  been 
elongated  by  a  stretching  strain. 

c.    The  Physiology  of  Bone  Moulding. 

Dr.  Koelliker  has  summarized  the  results  of  the 
observations  made  by  himself  and  his  predecessors  on 
the  processes  of  the  growth  and  absorption  of  bone, 
which  determine  the  forms  of  the  elements  of  the  skel- 
eton.1 

Bone  is  deposited  through  the  agency  of  uninuclear 
cells,  or  osteoblasts,  which  may  under  peculiar  condi- 
tions become  enlarged  and  multicellular,  when  they 
are  termed  osteoclasts.  These  osteoclasts  produce  an 
absorption  or  destruction  of  the  bone  or  dentine  with 
which  they  are  in  contact,  the  bone  or  dentine  being 
passive  under  the  operation.  How  this  is  done  is  not 
known.  Pieces  of  ivory  which  have  been  used  to  re- 
place bone  removed  by  surgical  methods,  have  been 
found  to  be  both  corroded  by  osteoclasts,  and  overlaid 
by  layers  of  living  bone  by  osteoblasts. 

In  explanation  of  the  causes  which  induce  the  for- 
mation and  action  of  the  osteoclasts,  Koelliker  remarks 
that :  "  the  totality  of  changes  of  the  jaws  during  the 
development  of  teeth  appears  to  show  that  it  is  pres- 
sure by  the  soft  parts  which  causes  the  absorption  of 
bone.  One  can  admit  in  the  case  of  the  jaw  that  the 
dental  sacs  in  process  of  growth  produce  by  their  en- 
largement a  state  of  irritation  in  the  layer  of  osteo- 
blasts which  originally  border  the  alveolar  edge,  and 

1  "  The  Normal  and  Typical  Absorption  of  Bones  and  Teeth,"   Verhandl. 
der  Phys.  Med.  Ges.  ran  M'iirzburg,  II.,  III.,  1872. 


286    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

that  in  consequence  of  this  irritation  the  cellules  trans- 
form themselves  into  osteoclasts,  and  acquire  a  new 
power,  that  of  absorbing  bone.  The  function  will 
cease  as  soon  as  the  teeth  are  formed,  by  the  termina- 
tion of  pressure,  and  then  the  formative  action  of  the 
cellules  adjacent  to  the  bone  will  repair  it  as  a  conse- 
quence of  a  retransformation  of  these  elements  into 
osteoblasts. 

"I  will  not  push  further  this  first  attempt  at  an 
explanation  of  the  normal  absorption  of  bone,  but  I 
content  myself  with  observing,  that  in  any  case,  pres- 
sure exercised  by  the  soft  parts  counts  for  much  in  this 
phenomenon.  Who  does  not  remember  in  the  face  of 
these  facts,  numerous  cases  of  pathological  absorption 
of  bone  due  to  aneurisms,  tumors,  and  hypertrophied 
organs?  Who  will  not  admit  the  great  effect  of  the 
disappearance  or  arrest  of  development  of  organs  on 
the  size  of  their  osseous  surroundings ;  as  Pick,  for- 
merly professor  of  anatomy  at  Marburg,  has  shown  to 
take  place  in  the  orbit  after  the  extirpation  of  the  eye? 
It  is  possible  to  go  a  step  further  in  the  proposition, 
that  external  pressure  has  much  to  do  with  absorp- 
tion. Thus  the  growth  of  the  brain  and  spinal  cord 
produce  the  resorption  seen  in  the  interior  of  the  skull 
and  of  the  spinal  canal  ;  that  of  the  eye  and  of  the 
nasal  mucosa,  and  of  the  cranial  vessels  and  nerves, 
have  resulted  in  the  enlargement  of  their  cavities  ;  and 
in  the  case  of  foramina,  in  their  wider  expansion.  .  .  . 
The  medullary  cavities  of  bones  are  produced  in  the 
process  of  growth  by  the  corrosive  activity  of  osteo- 
clasts." 

It  is  then  pressure  which  produces  the  excavations 
which  form  new  cotyli  in  the  construction  of  new  ar- 
ticulations due  to  dislocations.  By  such  excavations 


KINETOGENESIS.  287 

elevated  portions  remain  adjacent  to  them.  Other 
elevations,  as  already  described,  are  due  to  deposit  of 
bone  stimulated  by  the  absence  of  accustomed  pres- 
sure, as  in  the  filling  up  of  the  old  ulnar  cotylus  in 
the  human  subject  above  described.  Other  elevations 
or  osseous  deposits  such  as  occur  at  muscular  and 
ligamentous  insertions  appear  to  follow  a  pulling  stress. 

Many  other  examples  of  the  abnormal  production 
of  articulations  might  be  cited,  but  the  above  are  suf- 
ficient to  show  the  plasticity  of  osseous  tissue.  It  is 
also  evident  that  if  such  results  follow  the  stimulus  of 
the  parts  during  a  short  period  of  months  or  years, 
the  continuance  of  the  appropriate  mechanical  stresses 
through  geologic  ages  must  have  been  quite  sufficient 
to  produce  all  the  characters  which  we  observe  in  the 
articulations  of  the  vertebrate  skeleton. 

I  will  now  present  the  inferences  which  may  be  de- 
rived from  consideration  of  the  facts  hitherto  presented 
in  this  chapter.  We  have  not  been  witnesses  of  the 
process  of  evolution,  yet  we  believe  that  it  has  been 
in  active  operation.  We  have  not  been  able  to  observe 
its  modus  operandi,  but  we  may  safely  infer  what  it 
has  been  from  the  facts  which  are  before  us.  Kineto- 
genesis  having  been  observed  in  both  the  soft  sarcode 
(muscle)  and  in  the  hard  parts  of  animals,  the  law  of 
uniformity  obliges  us  to  believe  that  similar  changes 
have  taken  place  in  past  ages  whenever  the  necessity 
arose,  and  the  energy  at  nature's  disposal  was  suffi- 
cient. 

il.     MOULDING  OF  THE  ARTICULATIONS. 

a.   The  Limb  Articulations. 

This  part  of  the  subject  has  the  advantage  of  many 
facts  of  paleontology  in  our  possession.  We  have 


288    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


now  discovered  the  outlines  of  the  phylogeny  of  many 
mammalian  types,  and  many  detailed  histories  of  spe- 
cial lines  of  descent  are  known.  Our  knowledge  is 
most  complete  in  the  unguiculate  and  ungulate  pla- 

centals,  while  it  is  least 
as  regards  the  Mutilata, 
and  the  implacentals.  We 
have  excellent  series  of 
skeletal  parts,  and  I  have 
given  the  successional 
modifications  of  some  of 
them  on  page  139. 

In  the  first  place,  I 
will  select  an  illustration 
of  the  effects  of  use  on 
the  articulations  of  the 
limbs  and  feet  of  the 
Mammalia.  I  take  first 
the  ankle  and  wrist-joints. 
In  the  ruminating  animals 
(ox,  deer,  camel,  etc.)  and 
in  the  horse,  among  other 
living  species,  the  ankle- 
joint  is  a  very  strong  one, 

j  j       -,  r 

^nd  yet    admits    of    an    CX- 

tensive  bending  of  the  foot 
ing  pentadactyle  plantigrade  foot  with-  .,        i  j      .  treU]e 

out   groove    of    astragalus,  as   in    the    C 
probable   ancestor  of  the  Diplarthra.     tOngUC-and-grOOVC    joint  ; 

that   is,  two   keels  of  the 

first  bone  of  the  foot,  the  astragalus,  fit  into  two  grooves 
of  the  lower  bone  of  the  leg,  the  tibia,  while  between 
these  grooves  a  keel  of  the  tibia  descends  to  fill  a  cor- 
responding groove  of  the  astragalus.  Such  a  joint  as 
this  can  be  broken  by  force,  but  it  cannot  be  dislocated. 


Fig.  68. — Periptychus  rhabdodon 
Cope,  a  condylarthrous  genus  of  the 
Puerco  epoch  of  New  Mexico;  poste- 
rior foot,  one-half  natural  size,  show- 


KINE  TO  GENESIS.  289 

Now,  in  all  bones  the  external  walls  are  composed  of 
dense  material,  while  the  centers  are  spongy  and  com- 
paratively soft.  The  first  bone  of  the  foot  (astragalus) 
is  narrower,  from  side  to  side,  than  the  tibia  which 
rests  upon  it.  Hence  the  edges  of  the  dense  side-walls 
of  the  astragalus  fall  within  the  edges  of  the  dense 
side-walls  of  the  tibia,  and  they  have  pressed  into  the 
more  yielding  material  that  forms  the  end  of  the  bone, 
and  causing  bone  absorption,  pushed  it  upward,  thus 
allowing  the  side-walls  of  the  tibia  to  embrace  the 
side-walls  of  the  astragalus.  Now,  this  is  exactly  what 
would  happen  if  two  pieces  of  plastic  dead  material, 
similarly  placed,  should  be  subjected  to  a  continual 
pounding  in  the  direction  of  their  length.  And  in 
view  of  the  facts  already  cited  we  cannot  ascribe  any 
other  immediate  origin  to  it  in  the  living  material. 

The  same  active  cause  that  produced  the  two 
grooves  of  the  lower  end  of  the  leg  produced  the  groove 
of  the  middle  of  the  upper  end  of  the  astragalus.  Here 
we  have  the  yielding  lower  end  of  the  tibia  resting  on 
the  equally  spongy  material  of  the  middle  of  the  as- 
tragalus. There  is  here  no  question  of  the  hard  ma- 
terial cutting  into  soft,  but  simply  the  result  of  con- 
tinuous concussion.  The  consequence  of  concussion 
would  be  to  cause  the  yielding  faces  of  the  bones  to 
bend  downward  in  the  direction  of  gravity,  or  to  re- 
main in  their  primitive  position  while  the  edges  of  the 
astragalus  were  pushed  into  the  tibia.  If  they  were 
flat  at  first  they  would  begin  to  hollow  downward,  and 
a  tongue  above  and  groove  below  would  be  the  result. 
And  that  is  exactly  what  has  happened.  This  inclu- 
sion of  the  astragalus  in  the  tibia  does  not  occur  in  the 
reptiles,  but  appears  first  in  the  Mammalia,  which  de- 
scended from  them.  See  Figs.  68-69.  I  have  shown 


2go    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


that  without  exception,  every  line  of  Mammalia  com- 
menced with  types  with  an  astragalus  which  is  flat  in 
the  transverse  direction,  or  without  median  groove. 


n 


IN  W  1® 

w  r 


Fig.  69.  Fig.  70. 

Fig.  69. — Hind  foot  of  primitive  cameloid  Poebrotherium  labiatum  Cope, 
showing  grooved  astragalus  and  first  toe-bones  without  keel  in  front  at  lower 
end.  (From  Colorado.) 

Fig.  70.- — Hind  foot  of  three-toed  horse  (Prothippus  sejunctus  Cope;  (from 
Colorado),  showing  grooved  astragalus,  and  trace  of  keel  on  front  of  lower 
end  of  first  bone  of  middle  toe. 


KINETOGENESIS. 


291 


From  early  Tertiary  times  to  the  present  day,  we  can 
trace  the  gradual  development  of  this  groove  in  all 
the  lines  which  have  acquired  it.  The  upper  surface 
became  first  a  little  concave  ; 
the  concavity  gradually  became 
deeper,  and  finally  formed  a  well- 
marked  groove. 

The  history  of  the  wrist-joint  is 
similar.  The  surface  of  the  fore- 
arm bones  which  joins  the  fore- 
foot is  in  the  early  Tertiary  Mam- 
malia uniformly  concave.  In  the 
ruminating  mammals  it  is  divided 
into  three  fossae,  which  are  sep- 
arated by  sharp  keels.  These  fos- 
sae correspond  with  the  three 
bones  which  form  the  first  row  of 
the  carpus  or  palm.  The  keels 
correspond  to  the  free  sutures  be- 
tween them.  The  process  has  been 
evidently  similar  to  that  which  has 
been  described  above  as  produc- 
ing the  side-grooves  in  the  end  of 
the  tibia.  The  dense  walls  of  the 
sides  of  the  three  bones  imping- 
ing endwise  on  the  broad  yielding 

surface  of  the   fore-arm    (radius)   bones  of' two  middle  toes 
have  gradually,  under  the  influence   °f  deer-antel°P*  <&**?* 

'  Jurcatus    Leidy),    showing 

Of       COUntleSS       bloWS,       impressed    extension  of  keel  on  front 

themselves    into   the    latter.     On   of  lower  end    (From  Mio- 

cene  of  Nebraska. 

the    contrary,   the    surface   above 

the  weaker  lines  between  the  bones  not  having  been 

subject  to  the  impact  of  the  blows,  and  influenced  by 


Fig.   71.  — United    first 


292    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


gravity,  remains  to  fill  the 
grooves,  and  to  form  the 
keels  which  we  observe.  (See 
Fig.  72.) 

There  is  another  striking 
instance  of  the  same  kind  in 
the  feet  of  Mammalia ;  that 
is,  in  the  development  of  the 
keels  and  grooves  which  ap- 
pear at  the  articulation  of  the 
first  set  of  bones  of  the  toes 
(metapodials)with  the  bones 
of  the  second  set  (phalanges). 
These  keels  first  appear  on 
the  posterior  side  of  the  end 
of  the  first  set  of  bones,  pro- 
jecting from  between  two 
flexor  tendons.  These  ten- 
dons, in  many  mammals,  con- 
tain two  small  bones,  one  on 
each  side,  each  of  which  acts 
like  the  knee-pan,  and  resem- 
bles it  in  miniature,  which  are 
called  sesamoid  bones.  These 
tendons  and  bones  exercise 
a  constant  pressure  on  each 
side  of  the  middle  line,  when 
the  animal  is  running  or 
walking,  and  this  pressure, 
together  with  the  concussion 
with  the  ground,  appears  to 
have  permitted  the  protru- 
sion of  the  middle  line  in  the 
form  of  a  keel,  while  the 


KINETOGENESIS.  293 

lateral  parts  have  been  supported  and  even  com- 
pressed. The  reptilian  ancestors  of  the  mammals  do 
not  possess  these  keels. 

Now,  I  have  shown  that  the  lines  of  mammalian 
descent  displayed  by  paleontology  are  characterized, 
among  other  things,  in  most  instances,  by  the  gradual 
elevation  of  the  heel  above  the  ground,  so  that  the 
animal  walks  on  its  toes.  It  is  evident  that  in  this 
case  the  concussion  of  running  is  applied  more  directly 
on  the  ends  of  the  bones  of  the  foot  than  is  the  case 
where  the  foot  is  horizontal.  As  a  consequence  we 
find  the  keel  is  developed  farther  forward  in  such  ani- 
mals. But  in  many  of  these,  as  the  Carnivora,  hip- 
popotamus, and  the  camels,  there  is  developed  under 
the  toes  a  soft  cushion,  which  greatly  reduces  this  con- 
cussion. In  these  species  the  keel  makes  no  further 
progress.  In  other  lines,  as  those  of  the  horse,  the 
pig,  and  of  the  ruminants,  the  ends  of  the  toes  are  ap- 
plied to  the  ground,  and  are  covered  with  larger  hoofs, 
which  surround  the  toe,  and  the  cushion  is  nearly  or 
quite  dispensed  with.  These  animals  are  especially 
distinguished  by  the  fact  that  their  metapodial  keels 
extend  entirely  round  the  end  of  the  bone,  dividing 
the  front,  as  well  as  the  end  and  back  (Fig.  71)  ;  since 
the  front  of  the  metapodial  is  out  of  the  reach  of  the 
sesamoid  bones,  its  keel  would  seem  to  be  a  mould- 
ing to  the  groove  of  the  first  phalange,  which  is  itself 
moulded  by  the  middle  and  posterior  part  of  the  meta- 
podial keel  (Wortman.) 

A  third  and  similar  example  is  furnished  by  the 
elbow-joint  of  the  Quadrumana  and  Diplarthra.  In 
the  lower  Mammalia,  including  the  Carnivora  (Fig. 
73),  the  distal  end  of  the  humerus  presents  a  subme- 
dian  groove,  which  receives  the  ulna,  and  on  the  inner 


294    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


side  of  it,  a  more  or  less  convex  surface,  which  is  ap- 
plied to  the  head  of  the  radius.  The  coronoid  process 
of  the  ulna  is  narrow,  and  its  dense  bounding  walls 
impinge  on  the  broad  face  of  the  humeral  condyle  in 
flexion  and  extension,  and  transfers  to  it  the  force  of 
impact  when  the  foot  strikes  the  ground.  In  either 
case  strong  pressure  has  been  brought  to  bear  on 
the  humeral  condyle,  and  it  has 
yielded  to  the  denser  body  of  the 
ulna,  thus  forming  the  groove  in 
question.  In  such  Mammalia  the 
effect  of  impact  of  the  limb  on  the 
ground  has  been  to  impress  the 
head  of  the  radius  on  the  humeral 
condyle  upwards.  The  dense 
edges  of  the  former  have  im- 
pressed themselves  on  the  latter, 
while  the  unsupported  middle 
portion  has  yielded  in  the  direc- 
tion of  gravity,  and  the  result  is 
what  we  find,  i.  e.,  a  cup-shaped 
surface  of  the  head  of  the  radius, 
and  a  convexity  of  the  humeral 
condyle  adapted  to  it. 

Among  specializations  of  the 
elbow-joint,  I  call  attention  to 
two.  In  Quadrumana  the  head  of 
the  radius,  probably  owing  to  continued  supination  of 
the  manus,  occupies  a  position  at  the  external  side  of 
the  coronoid  process  of  the  ulna,  and  impinges  on  the 
outer  part  of  the  condyle  of  the  humerus.  The  con- 
cavity of  its  head,  and  the  convexity  of  the  humeral 
condyle,  are  visible  as  before,  but  a  prominent  tongue 
or  keel,  which  has  been  called  the  intertrochlear  crest, 


hyena)  seen  from  behind  ;  h, 
humerus ;  r,  radius ;  «,  ulna. 
Original. 


KINETOGErNESIS. 


295 


separates  the  ulnar  and  radial  surfaces  of  the  humerus 
(Fig.  74).  This  keel  occupies  the  groove  or  interval 
which  separates  the  head  of  the  radius  from  the  coro- 
noid  process  of  the  ulna.  It  is  plain  that  we  have  here 
another  tongue  and  groove-joint,  produced  by  the  mu- 
tual adaptation  of  parts  under  strain,  pressure,  and 
impact.  The  other  extreme  of  elbow-joint  is  found  in 
that  of  the  diplarthrous  Ungulata  (Fig.  75).  Here  the 
head  of  the  radius,  while  retaining  its  normal  position 
on  the  inner  side  of  the  fore-arm,  is  extended  to  the 
external  side  of  the  ulna  and 
even  beyond  it,  adapting  it- 
self to  the  entire  width  of  the 
humeral  condyles.  The  same 
structure  is  found  in  the  spe- 
cialized forms  of  both  series 
of  Diplarthra,  the  Perisso- 
dactyla  and  Artiodactyla. 
This  expansion  of  the  head  of 
the  radius  appears  to  be  in  di- 
rect relation  to  the  duration 

through    long    geologic    ages  Fig.  74.— Elbow-joint  of  chim- 

of  the  impacts  which  have  Panzeefrombe 
affected  the  limbs  of  these,  the  swiftest  of  the  Mam- 
malia. That  the  head  of  the  radius  should  be  spread 
so  as  to  fit  the  entire  surface  of  the  humerus,  under  all 
circumstances,  seems  to  be  a  mechanical  necessity. 
But  in  addition  to  this  we  find  a  tongue- and-groove 
adaptation,  in  which  the  crest  (which  I  have  called  the 
trochlear  crest)  articulates  with  a  groove  in  the  head 
of  the  radius.  The  internal  articulation  of  the  humerus 
with  the  radius  has  the  usual  form,  convex  and  con- 
cave distad.  The  trochlear  crest  marks  the  external 
border  of  the  olecranar  groove  of  the  humerus.  But 


2g6    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


the  external  part  of  the  humeral  condyles  is  converted 
into  a  roller  which  is  set  off  from  the  trochlear  crest  by 
the  abrupt  contraction  of  its  diameter  ;  while  the  cor- 
responding part  of  the  head  of  the  radius  projects  to 
fit  it  exactly. 

A  probable  explanation  of  the  form  of  this  roller 
may  be  derived  from  a  consideration  of  the  almost 
identical  structure  of  the  meta- 
podio-phalangeal  articulation  of 
the  Artiodactyla.  The  internal 
and  external  sides  of  the  distal 
metapodial  condyles  are  not  sim- 
ilar, the  external  being  more 
strongly  impressed  than  the  in- 
ternal (Fig.  77D).  This  is  simply 
due  to  the  unequal  pressure  ex- 
erted on  the  two  extremities  of 
the  condyle  by  the  phalanges, 
owing  to  the  divergent  direction 
of  the  digits  when  serving  as  a 
support.  In  the  distal  end  of 
}  the  humerus  the  same  effect  is 

Fig.  ys.-Efbow-oim  of  seen>  the  external  part  of  the  con- 


eiaphus   (red  deer)   dyle  nearly  resembling  the  corre- 
sponding part  of  the  metapodial 

bones.  This  is  traceable  to  the  same  cause,  viz.  :  the 
divergent  position  assumed  by  the  fore  arm  on  the  hu- 
merus, when  the  weight  is  supported  on  one  fore  leg 
only.  This  brings  the  line  of  pressure  through  the  ex- 
ternal part  of  both  the  head  of  the  radius  and  the  hu- 
meral condyle  (Fig.  77  A).  That  the  higher  ungulates 
are  "knock-elbowed"  may  be  readily  observed  by 
watching  their  gaits  (Fig.  76). 


KINE  TOGENESIS. 


297 


A  distinct  consequence  of  combined  impact  and 
strain  is  seen  in  the  evolution  of  the  carpus  and  tarsus 
of  the  Diplarthra.  In  primitive  Mammalia,  as  in 
most  Unguiculata,  the 
bones  of  the  carpus 
and  tarsus  succeed 
each  other  in  such  a 
way  that  the  principal 
lines  of  separation  be- 
tween the  elements 
coincide  in  the  two 
rows,  thus  producing 
a  linear  relation  be- 
tween the  former.  In 
the  Diplarthra,  on  the 
other  hand,  the  ele- 
ments of  the  two  rows 
alternate  with  each 
other  so  as  to  produce 
a  strong  interlocking. 
I  have  shown  that  in 
the  primitive  Ungu- 
lata,  the  Taxeopoda, 
the  linear  arrange- 
ment is  observed, 
while  in  three  orders 
of  ungulates,  the  Pro- 
boscidea,  Toxodontia, 
and  Amblypoda,  there 
are  various  degrees  of 
alternation  intermediate  between  the  linear  type  of  the 
Taxeopoda  and  the  completely  interlocked  condition 
of  the  Diplarthra.  It  has  been  already  pointed  out  in 
the  chapter  on  phylogeny  that  the  taxeopodous  type 


Fig.  76. — Cervus  canadensis  in  motion  : 
from  Muybridge's  Animal  Motion  ;  showing 
the  "  knock-elbow"  position  of  the  fore  leg, 
in  both  plantation  and  recover. 


298    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

of  foot  preceded  the  diplarthrous  in  time.  Besides  the 
alternation  mentioned,  it  is  quite  general  in  both  types 
for  the  metapodial  bones  to  possess  a  facet  for  con- 
tact with  that  element  of  the  carpus  and  tarsus  next 
exterior  to  the  one  to  which  they  have  their  principal 
articulation.  From  these  facts  it  is  evident  that  the 
bones  of  the  second  carpal  and  tarsal  rows  have,  in 


Fig.  77. — Cervus  elaphus;  A,  B,  C,  humero-radial  articulation  ;  A  and  B, 
with  the  radius  in  position;  C,  with  radius  twisted;  D.  £,  metatarsophalan- 
geal  articulation  ;  D,  front ;  E,  distal  view,  twisted. 

the  process  of  evolution,  assumed  a  position  interior 
to  their  primitive  position,  with  reference  to  the  first 
row  proximad  to  them,  and  the  metapodials  distad  to 
them.  The  cause  of  this  shifting  of  position  is  to  be 
found  in  the  movements  of  the  limbs  in  progression, 
and  especially  in  rapid  progression  (Fig.  78). 

If  we  observe   the  movements  of  the  limbs  in  a 


KINE  TO  GENESIS. 


299 


diplarthrous  ungulate,  we  shall  see  that  as  the  foot  is 
planted  on  the  ground  the  prominent  flexures  of  the 
limbs,  the  elbow  and  gambril  joints,  are  turned  in- 


follex     Index       X&JA       -inn?    Mininf 


Index 


Sled* 


Fig.  78. — Diagram  of  carpus  of  a  Taxeopod  (A)  and  (B)  of  a  diplarthrous 
ungulate.     From  Osborn. 

wards,  so  that  the  limb,  were  it  free  from  the  ground, 
would  be  twisted  or  rotated  on  its  long  axis  from 
within,  forwards  and  outwards.  As  the  foot  rests  on 


Fig-  79- — Raccoon  pacing,  showing  right  fore  foot  just  before  recovery. 
From  H.  Allen. 

the  ground,  the  limb  experiences  a  torsion  strain  in 
the  directions  mentioned.  This  throws  the  weight  on 
the  interior  bones  of  the  lower  legs,  the  radius  and  the 
tibia.  Thus  these  bones  have  acquired  a  great  supe- 


300 


PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


riority  in  dimensions  over  the  external  elements  (ulna 
and  fibula)  in  all  the  Diplarthra.  The  bones  of  the 
inner  side  of  the  first  carpal  and  tarsal  rows  have  thus 
transmitted  an  ever-increasing  share  of  the  impact,  as 
the  radius  and  tibia  have  developed,  and  have  grown 


Fig.  80.  Fig.  81. 

Fig.  80. — Rhinocerus  unicornis  carpus.  Arrow  ending  in  P,  line  of  impact 
in  plantation ;  do.  ending  in  A',  line  of  strain  in  recover. 

Fig.  81. — Eguus  cabaUus  forefoot.  Sc,  scaphoid;  L,  lunar;  Cu,  cunei- 
form; Toz,  trapezium  and  trapezoideo  ;  Un,  unciform  ;  ing.,  magnum-. 

with  their  growth  at  the  expense  of  the  external  ele- 
ments, the  cuneiform  in  the  carpus,  and  the  calcaneum 
in  the  tarsus,  which  have  become  very  narrow  elements 
in  the  higher  Diplarthra.  As  the  pressure  has  been 
obliquely  from  within  outwards,  the  growth  of  the 
proximal  elements,  the  scaphoid  and  lunar  in  front, 


302    PR  IMA  RY  FAC  TORS  OF  OR  GA  NIC  E  VOL  UTION. 

and  the  astragalus  behind,  has  been  in  the  same  direc- 
tion. It  has  been  shown  by  Dr.  H.  Allen  that  just 
before  the  recover  of  the  foot,  the  latter  is  directed 
outwards  from  a  line  parallel  with  the  axis  of  the  body, 
so  that  the  weight  falls  on  the  inner  part  of  the  sole  of 
the  former.  This  naturally  causes  the  bones  of  the 
foot  to  press  inwards  on  the  heads  of  the  metapodials, 
so  that  the  latter  tend  to  grow  outwards  on  the  second 
tarsal  row.  In  this  way  were  produced  the  facets  on 
the  external  side  of  the  heads  of  the  metapodials. 
Thus  is  accounted  for,  on  simple  mechanical  princi- 
ples, the  phenomenon  of  carpal  and  tarsal  displace- 
ment exhibited  in  its  highest  development,  by  the  Dip- 
larthra. 

It  is  significant  that  diplarthrism  has  not  appeared 
in  mammals  which  possess  an  elastic  pad  of  connec- 
tive tissue  on  the  soles,  as  in  Unguiculata  generally, 
and  especially  in  the  Carnivora.  Diplarthrism  is  pres- 
ent in  the  camels,  which  have  a  pad,  but  I  have  shown 
that  this  pad  did  not  appear  until  a  comparatively  late 
geologic  epoch,  and  long  after  diplarthrism  had  be- 
come established  in  the  camels'  ancestors,  the  Poe'bro- 
theriidae. 

The  faceting  of  the  head  of  the  astragalus  as  the 
result  of  impacts,  is  seen  on  comparison  of  the  astra- 
gali of  Phenacodus  and  Hyracotherium  in  Ungulata 
(Figs.  33-35),  and  of  Dissacus  and  Mesonyx  among 
the  Creodonta.  In  this  last  genus  we  have  the  only 
faceted  astragalus  among  carnivorous  mammals,  but 
this  genus  is  at  the  same  time  subungulate. 

b.    The  Forms  of  Vertebral  Centra. 

The  mutual  articulations  of  the  vertebral  column 
are  those  of  the  centra  and  of  the  zygapophyses.  Many 


KINETOGENESIS.  303 

important  modifications  in  these  articulations  are  to  be 
seen  in  Vertebrata,  the  Reptilia  presenting  the  great- 
est variety,  excepting  in  the  zygapophyses,  which  are 
tolerably  uniform  in  that  class.  In  the  Mammalia, 
modifications  of  the  central  articulations  are  not  more 
striking  than  are  those  of  the  zygapophyses. 

The  forms  of  central  articulation  are  four,  viz. :  the 
amphicoelous,  the  ball-and-socket,  the  plane,  and  the 
saddle-shaped.  The  first  type  is  only  seen  in  a  very 
imperfect  degree  in  Mammalia  and  in  but  very  few 
vertebrae,  where  it  is  indeed  but  a  modification  of  the 
plane.  The  ball-and-socket  is  chiefly  found  in  the 
neck  of  the  long-necked  Mammalia,  as  the  higher 
Diplarthra,  and  to  a  less  degree  in  their  lumbar  re- 
gions, while  the  dorsal  vertebrae  present  an  approach 
to  the  same  type  in  the  same  groups.  The  saddle- 
shaped  centrum  is  only  found  in  Mammalia  in  the 
necks  of  certain  genera  of  monkeys.  The  majority  of 
Mammalia  present  the  plane  articulation  of  all  the  ver- 
tebral centra. 

In  Mammalia  in  which  movement  of  the  vertebrae 
on  each  other  has  become  impossible,  the  centra  co- 
ossify,  as  for  instance  in  the  sacrum.  In  this  region  the 
number  of  vertebrae  coosified  is  directly  as  the  length 
of  the  iliac  bone,  which  supports  and  holds  them  im- 
movable. Such  is  their  condition  throughout  the 
dorsal  region  in  the  extinct  Edentata  of  the  family 
Glyptodontidae,  where  the  carapace  is,  as  in  the  tor- 
toises, inflexible,  and  which  therefore  limits  the  possi- 
bility of  motion  of  the  vertebral  column.  Another 
illustration  is  seen  in  the  necks  of  the  balaenid  Ceta- 
cea,  and  to  some  degree  in  the  Delphinidae  and  Physe- 
teridae.  The  lack  of  present  mobility  of  this  part  of 
the  column  is  due  to  its  extreme  abbreviation,  a  char- 


304    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

acter  which  has  been  gradually  developing  during  Ce- 
nozoic  time  ;  since  the  earliest  Cetacea  had  consider- 
ably longer  necks  than  the  later  ones,  and  had  their 
vertebral  centra  distinct.  It  appears  to  me  probable 
that  the  shortening  was  the  result  of  disuse.  This 
disuse  would  arise  from  gradually  increasing  powers 
of  locomotion  through  the  water,  a  progress,  which, 
judging  from  the  character  of  the  limbs  of  the  Zeuglo- 
don,  was  evidently  made  after  the  time  of  the  Eocene. 
The  increase  of  speed  would  enable  the  animal  to  over- 
take and  capture  its  prey,  without  the  necessity  of 
using  a  long  prehensile  neck  in  seizing  it  in  the  pur- 
suit. 

The  ball-and-socket  articulation  of  the  vertebrae  is 
well  known  to  be  the  predominant  condition  in  the 
Reptilia,  and  the  fact  that  it  is  necessarily  associated 
with  the  flexibility  of  the  column  is  equally  well  under- 
stood. The  flexibility  is  directly  as  the  weakness  of 
the  limbs,  for  in  the  large  and  long-limbed  terrestrial 
Reptilia  of  the  order  Dinosauria,  the  vertebral  articu- 
lations of  the  dorsal  region,  at  least,  are  plane.  That 
it  is  chiefly  confined  to,  and  best  developed  in,  the 
most  flexible  regions,  i.  e.,  the  cervical  and  lumbar,  of 
the  column  of  the  Mammalia,  also  shows  this  neces- 
sary connection.  There  can  be  no  doubt  but  that  the 
ball-and-socket  vertebral  articulation  has  been  pro- 
duced by  constant  flexures  of  the  column  in  all  direc- 
tions, as  has  been  suggested  by  Marsh. 

iii.     INCREASE  OF  SIZE  THROUGH  USE. 

Under  this  head  I  enumerate  examples  where  the 
mechanical  causes  in  operation  are  less  self-evident 
than  those  included  under  the  preceding  section.  They 


KINE  TO  GENESIS.  305 

are,  however,  probably  due  to  the  same  process,  viz., 
impact  and  strain. 

a.    The  Proportions  of  the  Limbs  and  of  Their  Segments. 

The  length  of  the  legs  of  terrestrial  Mammalia  has 
increased  with  the  passage  of  time.  The  inferior  types 
of  Mammalia  now  existing,  as  Marsupialia,  Glires, 
Insectivora,  Edentata,  have  short  legs,  with  a  few 
cases  of  extreme  specialization  as  exceptions,  such  as 
kangaroos,  rabbits,  and  jerboas  (hiad  legs  only),  the 
Dolichotis  patachonica,  the  Rhynchocyonidae,  and  the 
sloths.  In  the  orders  which  stand  at  the  summit  of 
the  series,  as  the  Diplarthra,  Proboscidia,  Carnivora, 
and  Anthropomorpha,  the  legs  are  much  increased  in 
length,  and  this  is  especially  marked  in  certain  forms 
which  stand  in  all  respects  at  the  summit  of  their  re- 
spective orders.  Thus  in  Diplarthra,  the  deer,  ante- 
lope, and  horse  are  distinguished  for  length  of  limb ; 
in  the  Proboscidia,  the  elephant ;  in  the  Carnivora, 
the  large  cats  and  hyaenas ;  in  the  Anthropomorpha, 
the  fore  limbs  are  long  in  all,  the  hind  ones  especially 
so  in  man. 

The  cause  of  this  elongation  is  apparently  use.  It 
is  the  hind  legs  that  are  elongated  in  a  straight  line  in 
animals  that  walk  on  them,  as  man  ;  and  both,  in  those 
that  walk  on  both,  as  the  elephant.  In  animals  that 
leap  with  the  hind  legs  these  are  still  more  elongated, 
and  are  folded  when  at  rest,  and  rapidly  extended 
when  in  motion.  In  animals  that  climb  with  the  fore 
legs,  these  are  elongated,  as  in  the  Anthropomorpha, 
except  man.  In  those  that  climb  with  all  fours,  all 
are  elongate,  as  in  the  sloths.  It  must  be  remembered 
that  these  elongations  are  the  sum  of  increments  added 
one  to  the  other  through  long  ages  of  use  in  geologic 


306    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

time.  The  mechanical  character  of  that  use  has  not 
been  identical.  It  is  of  two  principal  kinds,  viz. :  im- 
pact and  longitudinal  strain.  These  two  forms  of  en- 
ergy move  in  directions  opposite  to  each  other ;  the 
one  as  compression  in  the  direction  of  the  length  of 
the  bone ;  the  other,  as  a  stretching  in  the  direction  of 
the  length  of  the  bone.  Both  processes  alike  appear 
to  have  stimulated  growth  in  the  direction  of  the  length 
of  the  bone. 

The  increase  in  the  length  of  the  legs  has  not  been 
always  due  to  increase  in  length  of  the  same  segment. 
In  a  majority  of  the  higher  mammals,  the  increase  has 
been  principally  in  the  foot,  and  especially  in  the  meta- 
podials  and  digits,  producing  digitigradism.  In  the 
forms  which  have  remained  plantigrade,  the  femur 
(Proboscidia),  or  femur  and  tibia  (Quadrumana),  or 
all  three  segments  (Tarsius),  have  been  the  seat  of  the 
elongation.  We  can  again  trace  these  especial  elonga- 
tions to  special  uses.  In  animals  which  leap,  the  dis- 
tal segments  of  the  limbs  are  elongated ;  in  those 
which  do  not  leap,  but  which  merely  run  or  walk,  it  is 
the  proximal  segments  of  the  limbs  which  are  elon- 
gated. 

Animals  which  run  by  leaping  are  divided  into 
those  which  run  and  leap  with  all  fours,  as  Diplarthra ; 
and  those  which  run  and  leap  with  the  posterior  limbs 
only,  as  the  jerboas  and  kangaroos.  In  both  types, 
the  distal  segments  of  the  hind  limb  are  elongated,  and 
in  the  Diplarthra,  those  of  the  fore  limb  also.  , 

Animals  which  do  not  leap  in  progression  (ele- 
phants, Quadrumana,  bears)  are  always  plantigrade, 
and  have  very  short  feet,  but  elongate  thighs,  and, 
mostly,  tibias. 

These  facts  show  that  those  elements  which  receive 


KINE  TOGENESIS. 


307 


the  principal  impact  in  progression  are  those  which 
increase  in  length.  In  digitigrade  animals  it  is  the  feet 
which  receive  the  impact  of  the  repeated  blows  on  the 


Mb  i 


Fig.  83. — Pes  of  (A)  Merychochcerus  montanus  from  Scott ;  (B]  Bos  taurus, 
much  reduced.  Co.,  Calcaneum  ;  As,  Astragalus;  Na,  Navicular;  Neb,  Na- 
viculocuboid  ;  Cu,Mec,  Ecto-mesocuneiform ;  Mt,  Metatarsals  (cannon  bone); 
Enc,  Entocuneiform. 

earth  while  in  progression,  while  supporting  the  weight 
of  the  body  at  every  stage  of  the  process.  In  planti- 
grade animals  it  is  the  soles  of  the  feet,  and  the  bones 
of  the  leg  in  line  with  them,  which  receive  the  impact, 


3o8    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION-. 


KINETOGENESIS.  309 

while  the  feet  beyond  this  point  receive  none,  and  do 
not  support  the  body,  except  very  partially  at  the  mo- 
ment of  leaving  the  earth. 

b.    The  Number  of  the  Digits. 

The  reduction  in  the  number  of  toes  is  supposed  to 
be  due  to  the  elongation  of  those  which  receive  the 
greater  number  of  strains  and  impacts  in  rapid  pro- 
gression, and  the  complementary  loss  of  material 
available  for  the  growth  of  those  not  subject  to  this 
stimulus.  This  is  rendered  probable  from  the  fact 
that  the  types  with  reduced  digits  are  dwellers  on  dry 
land,  and  those  that  have  more  numerous  digits  are 
inhabitants  of  swamps  and  mud,  or  are  more  or  less 
aquatic.  That  this  inequality  is  due  to  these  mechan- 
ical causes  is  still  further  indicated  by  the  fact  that  in 
those  forms  where  the  soles  are  thickly  padded  (Car- 
nivora,  Proboscidia)  the  reduction  has  either  not  taken 
place,  or  has  made  little  progress,  amounting  to  the 
loss  of  only  one  digit.  (An  apparent  exception  in  the 
case  of  the  camels  will  be  mentioned  later.)  A  still 
more  important  body  of  evidence  which  shows  that 
the  inequality  in  size  and  number  of  digits  is  due  to 
impacts  and  strains  unequally  distributed,  has  been 
brought  forward  by  Ryder.  He  points  out  that  defi- 
nite results  are  to  be  observed  in  those  limbs  of  a  given 
type  of  animal  which  experience  correspondingly  defi- 
nite influences ;  while  in  the  limbs  where  the  strains 
are  equal,  the  modifications  do  not  appear.  Examples 
of  this  kind  are  to  be  found  in  the  unguiculate  Mam- 
malia and  in  the  Marsupialia.  Thus  in  the  jerboas 
which  use  the  hind  limbs  in  leaping,  these  only  dis- 
play reduced  digits,  the  fore  limbs  remaining  of  prim- 


310    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


itive  character.     The  same  is  true  of  the  kangaroos. 
In  digging  genera,  the  fore  limbs  experience  the  modi- 


0 


Fig.  85. — A,  Right  posterior  foot  of  Prothippus  sejunctus  Cope,  from  Colo- 
rado, about  one-half  natural  size.  From  U.  S.  Geological  Survey  of  Territo- 
ries, F.  V.  Hayden,  IV.  B,  Right  posterior  foot  of  Poebrotherium  labiatum 
Cope,  from  Colorado,  three-fifths  natural  size.  From  Hayden's  Report,  IV., 
Plate  CXV. 

fications,  while  the  hind  limbs  are  more  normal,  as  in 
Chrysochloris  and  various  Edentata. 


KINETOGENESIS.  311 

Ryder  sums  up  the  evidence  in  two  propositions, 
as  follows  : l 

"I.  The  mechanical  force  used  in  locomotion  dur- 
ing the  struggle  for  existence  has  determined  the  digits 
which  are  now  performing  the  pedal  function  in  such 
groups  as  have  undergone  digital  reduction. 

"II.  When  the  distribution  of  mechanical  strains 
has  been  alike  upon  all  the  digits  of  the  manus  or  of 
the  pes,  or  both,  they  have  remained  in  a  state  of  ap- 
proximate uniformity  of  development." 

The  application  of  the  impact,  or  strain,  or  both, 
in  progression,  is  easily  understood.  In  recover  (see 
p.  299),  the  leg  is  bent  on  the  foot  as  it  rests  on  the 
ground,  and  those  digits  which  then  leave  the  ground 
last,  sustain  greater  strain  than  those  which  leave  it 
sooner.  In  replacing  the  foot  on  the  ground  (planta- 
tion), those  digits  which  strike  it  first  experience  greater 
force  of  impact  than  those  which  strike  it  later.  Sup- 
posing the  five  primitive  digits  to  have  been  of  equal 
length,  the  distribution  of  the  impact  and  of  the  strain 
will  depend  on  the  angle  at  which  the  foot  is  directed 
with  reference  to  the  direction  of  motion.  If  the  feet 
are  pointed  forwards,  the  middle  digits  will  experience 
strain  and  impact ;  if  outwards,  the  inner  digits  bear 
the  weight ;  if  inwards,  the  external  digits  receive  it. 

Observation  on  five-toed  plantigrade  mammals 
shows  that  their  feet  are  turned  neither  inwards  nor 
outwards  in  progression,  but  straight  forwards.  It  is 
probable  that  the  primitive  Mammalia  moved  in  the 
same  manner.  This  is  also  to  be  inferred  from  the 
fact  that  they  were  plantigrade,  so  that  the  leverage 
transversely  in  or  out  which  results  from  the  elevated 
heel  of  the  digitigrade  leg  was  very  much  less  in  them. 

^American  Naturalist,  1877,  p.  607. 


3i2    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

In  progression  of  this  type,  the  middle  digits  of  course 
leave  the  ground  last  and  strike  it  first.  Thus  the 
middle  toes  have  been  stimulated  at  the  expense  of  the 
lateral  ones,  so  that  in  the  Diplarthra,  either  the  mid- 


die  one  (Perissodactyla)  alone  remains,  or  the  middle 
two  (Artiodactyla).  In  the  kangaroos  the  external  toes 
have  been  chiefly  used,  so  that  the  fourth  and  fifth 
digits  have  been  principally  developed.  In  man,  who 


KINETOGENESIS.  313 

now  turns  his  feet  out  when  using  them  as  bases  of  re- 
sistance to  muscular  labor,  the  inner  digit  has  become 
most  robust.  The  mechanical  history  of  the  human 
great  toe  is  however  yet  unknown. 

As  regards  the  equal  development  of  the  third  and 
fourth  digits  in  the  Artiodactyla,  as  distinguished  from 
the  development  of  the  middle  digit  of  the  Perisso- 
dactyla,  I  have  advanced  the  following  hypothesis.  I 
have  supposed  that  the  primitive  members  of  this  for- 
mer division  sprung  from  pentadactyl  plantigrades  who 
dwelt  in  swamps  and  walked  on  very  soft  ground. 
The  effect  of  progression  in  mud  is  to  spread  the  toes 
equally  in  all  directions  and  on  each  side  of  the  me- 
dian line.  Such  feet  remain  in  the  mud-loving  hippo- 
potamus, and  to  a  lesser  degree  in  the  true  pigs.  From 
such  ancestry  the  cloven-footed  Diplarthra  derived 
their  characters.  The  Hyracotheriinae,  the  ancestors 
of  all  Perissodactyla,  display  on  the  other  hand  evi- 
dence of  a  life  on  harder  ground,  especially  in  the  pos- 
terior foot,  where  articulations  are  already  rigidly  de- 
fined, and  the  third  digit  is  longer  than  the  others. 
Some  of  their  descendants  love  swamps,  as  one  or  two 
species  of  tapirs  and  rhinoceroses,  but  others  live  on 
the  dryest  ground,  as  the  Andean  tapir  and  the  African 
rhinoceros.  As  to  the  highest  members  of  both  even 
and  odd  toed  groups,  the  Bovidae  and  the  Equidae, 
their  habitat  is  in  the  vast  majority  of  cases  the  dry 
land  (Figs.  80-81). 

Continued  and  excessive  prehensile  strain  with 
weight  on  the  longest  digits,  must  be  assigned  as  the 
cause  of  the  especial  elongation;  and  disuse  as  the 
cause  of  the  loss  of  the  external  and  shorter  digits,  of 
the  sloths ;  so  that  there  remain  but  two  and  three 
(Cholrepus  and  Bradypus),  and  in  the  climbing  ant- 


3i4    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION-. 

eater  (Cycloturus)  but  one  principal  toe  and  two  rudi- 
ments. The  excessive  strain  and  impact  experienced 
by  certain  digits  in  leaping,  accounts  for  the  digital 
reduction  in  the  hinder  foot  of  the  kangaroos  and  jer- 
boas, precisely  as  in  the  perissodactyle  ungulates. 

c.    The  Horns. 

Horns  are  developed  in  Mammalia  and  other  Ver- 
tebrata  on  similar  parts  of  the  skull,  principally  on  the 
posterior  lateral  angles,  as  in  various  Batrachia,  Rep- 
tilia,  and  Mammalia,  and  on  the  nose,  as  in  a  few 
Mammalia  and  several  reptiles,  recent  and  extinct. 
These  parts  are  the  ones  which  are  especially  brought 
into  contact  with  resisting  bodies  ;  the  nose  in  pushing 
a  path  or  way  for  the  head  and  body;  the  lateral  occi- 
pital region  in  defence  and  assault,  when  the  sensitive 
nose  and  eyes  are  protected  by  being  held  near  the 
ground.  In  the  latter  position  the  posterolateral  an- 
gles, when  present,  receive  more  frequent  collision 
with,  and  vigorous  stimulation  from,  a  body  attacked 
or  resisted,  and  in  accordance  with  the  observed  re- 
sults of  irritation  on  dermal  and  osseous  tissues,  addi- 
tional matter  has  been  deposited.  In  Lacertilia  and 
Batrachia  Salientia  there  are  distinct  posteroexternal 
cranial  angles ;  in  Batrachia  Urodela  such  angles  are 
less  prominent.  In  unguiculate  Mammalia  and  in  all 
others  with  a  sagittal  crest  there  are  no  such  angles ; 
hence  this  type  of  skull  has  never  developed  posterior 
horns.  The  rhinoceros  has  developed  the  dermal 
nasal  horn,  and  the  Elasmotherium,  a  median  osseous 
horn,  since  posterolateral  angles  of  the  skull  are  want- 
ing or  close  together.  In  the  Dinocerata  and  the  Ar- 
tiodactyla,  where  the  temporal  crests  are  lateral,  leav- 
ing a  wide  fronto-parietal  plane  with  posterior  lateral 


KINETOGENESIS.  315 

angles,  horns  are  developed.  In  members  of  both 
groups  horns  have  been  developed  over  the  orbits  also 
(Fig.  87),  and  in  the  Dinocerata  on  the  extremities  of 
the  nasal  bones  as  well.  These  growths  are  all  on 
parts  which  are  subject  to  especial  irritation  by  contact 
with  other  bodies,  animate  and  inanimate. 

Among  Artiodactyla,  the  deer  (Cervidae)  are  espe- 
cially distinguished  by  the  periodical  shedding  of  all 
but  the  bases  of  their  horns.  Extinct  forms  found  in 
the  Upper  Miocene  of  the  United  States  and  France 
(the  Loup  Fork  series)  furnish  the  explanation  of  the 
origin  of  this  remarkable  peculiarity.  In  the  genus 
Cosoryx  we  find  that  the  horns  may  or  may  not  pos- 
sess a  burr  near  the  base  of  the  beam,  like  that  of  the 
deer ;  the  same  species  being  indifferently  with  it  or 
without  it.  This  observation  has  been  made  on  three 
species, — the  C.  necatus,  C.  furcatus  and  C.  ramosus. 
The  following  explanation  of  these  facts  has  been  pro- 
posed by  myself.1  "From  the  facts  of  the  case  the 
following  inference  may  be  derived,  premising  that  it 
is  very  probable  that  a  genus  allied  to  the  present  one 
has  given  origin  to  the  family  of  the  deer.  It  is  ob- 
vious that  the  horns  of  (Dicrocerus)  Cosoryx  did  not 
possess  a  horny  sheath  as  in  the  Bovidae,  from  the  fact 
of  their  being  branched.  As  the  sheath  grows  by  ad- 
dition at  the  base,  the  presence  of  branches  which 
necessarily  obstruct  its  forward  movement,  would  be 
fatal  to  the  process.  There  is  much  to  be  said  in  favor 
of  the  view  that  the  horns  were  covered  with  an  integu- 
ment, probably  furred,  as  in  the  giraffe  and  young 
stage  in  the  deer.  Thus  there  are  grooves  in  the  sur- 
face of  the  beam  for  superficial  blood-vessels,  which 

1  U.  S.  G.  G.  Survey  West  of  the  tooth  Mer.,  G.  M.  Wheeler  :  IV.,  Paleon- 
tology, 1877,  p.  348. 


316    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


must  have  been  protected  by  skin  (I  do  not  observe 
these  grooves  on  the  beam  of  C.  teres}.  The  retention 
of  the  broken  extremity  of  an  antler,  so  as  to  be  re- 
united, as  described  (Fig.  87,  C),  could  not  have  been 
accomplished  without  an  integument.  The  presence 

of  the  burrs  cannot  be 
accounted  for  on  any 
other  supposition,  as 
there  are  no  foramina 
to  give  exit  to  nutrient 
vessels  at  the  point 
where  they  exist;  the 
irregularity  of  those 
positions  also  forbids 
the  latter  idea,  and 
adds  to  the  probability 
that  the  arteries  which 
furnished  the  deposit  of 
phosphate  of  lime  were 
contained  in  a  super- 
ficial dermal  coating. 
The  supposition  is  also 
strengthened  by  the  fact 
that  the  only  existing 
ruminants  (the  giraffes) 

Cosoryx  ramosus   Cope;    C,  antler  broken    with    permanent 


u.  s.  GO-V.  Geoi.  Expi.  tooth  Mer.,  G.  M. 


without  horny  sheaths 
have  them  covered  with 
hairy  skin. 

"  It  appears  that  in  the  antlers  of  the  Cosoryx  the 
deposit  of  a  burr  was  immediately  associated  with  the 
death  of  the  portion  of  the  horn  beyond  it,  so  that  it 
disintegrated  and  disappeared.  This  was  not  the  case 
with  the  beam  in  the  specimens  observed.  Neverthe- 


KINETOGENESIS.  317 

less  it  is  probable  that  the  death  of  the  horn  would  be 
associated  with  the  deposit  of  the  burr  in  this  case 
also,  were  the  conditions  the  same.  What  those  con- 
ditions were  we  can  only  surmise.  It  was  very  prob- 
ably the  death  of  the  integument  which  invested  and 
nourished  the  horn  that  produced  that  result ;  and 
this  would  more  readily  occur  in  the  exposed  antlers 
than  in  the  more  protected  basal  portion  of  the  beam. 
It  is  very  probable  that  this  result  would  follow  blows 
and  laceration  of  the  surface  received  during  combat, 
or  accidental  contact  with  hard  substances.  The  in- 
tegument would  be  stripped  up  to  near  the  junction  of 
the  antlers  with  each  other,  or  of  the  beam  with  the 
cranium,  and  the  arteries  would  be  constricted  or 
closed  at  those  points.  It  is  near  these  junctions  that 
all  of  the  burrs  are  found.  But  as  such  lesion  would 
be  necessarily  less  complete  at  the  point  where  the 
horn  has  greatest  circumference,  so  the  entire  death 
of  the  horn  might  be  less  usual  than  that  of  the 
branches.  Should  such  lesions  have  occurred  for  a 
long  period  at  the  breeding  season,  nature's  efforts  to 
repair  by  redeposit  of  bony  tissue  might  as  readily  be- 
come periodical  as  the  increase  in  size  and  activity  of 
the  reproductive  organs  and  other  growths  which  char- 
acterize the  breeding  season  in  many  animals.  The 
subsequent  death  of  the  horn  would  be  at  some  time 
followed  by  its  shedding  by  the  ordinary  process  of 
sloughing." 

Cosoryx  is  not  the  true  ancestor  of  the  Cervidae,  as 
its  teeth  have  already  attained  the  prismatic  type  of 
the  higher  Bovidae.  But  Blastomeryx  is  most  prob- 
ably the  ancestor  of  the  deer.  The  remains  of  this 
genus  occur  with  those  of  Cosoryx,  but  the  burr  has 
not  yet  been  observed  on  its  horns. 


318    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


IV.    THE  MECHANICAL  ORIGIN  OF  DENTAL  TYPES. 

In  investigating  the  origin  of  dental  types  it  is 
necessary  to  become  acquainted  with  the  nature  of  the 
mutual  movements  of  the  series  of  the  opposing  jaws. 
I  have  classified  them  as  follows  : * 

I.  Inferior  molars  work  within  superior  molars,  but  not  between 
them.     Psalidodect  mastication. 

1.  The  inferior  molars  shear  on  the  interior  side  of  the  su- 
perior :  Triconodontidce. 

II.  Part  or  all  of  inferior  molars  work  alternately  to  and  between 
superior  molars.     Amoebodect  mastication. 

2.  The  inferior  molar  shears  forwards  on  the  superior  mo- 
lar.    Proterotome  mastication  :      Creodonta;  Carnivora. 

3.  The  inferior  molars  shear  posteriorly  against  the  superior 
molars.     Opisthotome  mastication  : 

Coryphodontidcz,   Uintatheriidce. 

III.  Molar  teeth  of  both  jaws  oppose  each  other.     Antiodect  mas- 
tication. 

4.  The  movement  of  the  lower  jaw  is  vertical.    Orthal  mas- 
tication :  Suo'idea,  Tapiridce. 

5.  The  movement  of  the  lower  jaw  is  from  without  inwards. 
Ectal  mastication  :  many  Peris sodacty la. 

6.  The  movement  of  the  lower  jaw  is  from  within  outwards. 
Ental  mastication  : 

most  Artiodactyla;  some  Perrissodactyla. 

7.  The  movement  of  the  lower  jaw  is  from  before  backwards. 
Proal : 

some  Monotremata  Multituberculata  and  most  Glires. 

8.  The  movement  of  the  lower  jaw  is  from  behind  forwards. 
Palinal  :  Proboscidea  (Ryder). 

The  distinction  of  teeth  into  incisors,  canines,  and 
molars  appears  independently  at  various  points  in  the 
line  of  Vertebrata.  Incisors  and  molars  are  distin- 

IMechan.  Origin  Hard  Parts  of  Mammalia,  1889,  p.  226. 


KINETOGENESIS.  319 

guished  in  sparoid  fishes,  and  in  placodont  and  dia- 
dectid  reptiles.  Canine-like  teeth,  or  pseudo-canines, 
appear  in  clepsydropid  and  crocodilian  reptiles,  and 
in  saurodont  fishes.  Canine-like  incisors  appear  in 
the  Clepsydropidae.  The  variety  of  character  in  these 
structures  presented  by  the  Mammalia  to  be  consid- 
ered is  great,  and  the  principles  deduced  from  obser- 
vation of  them  are  applicable  to  the  Vertebrata  in 
general. 

As  mechanical  causes  of  the  origin  of  dental  modi- 
fications, I  have  enumerated  the  following  : 

1.  Increase  of  size  of  a  tooth,  or  a  part  of  a  tooth, 
is  due  to  increased  use,  within  a  certain  maximum  of 
capacity  for  increased  nutrition. 

2.  The  change  of  direction  and  use  of  a  tooth  take 
place  away  from  the  direction  of  greatest,  and  in  the 
direction  of  least  resistance. 

3.  It  follows,   from   their  greater  flexibility,   that 
crests  of  crowns  of  teeth  yield  to  strains  more  readily 
than  do  the  cusps. 

4.  The  increase  in  the  length  of  crests  and  cusps 
in  all  directions,  and  therefore  the  plications  of  the 
same,  is  directly  as  the  irritation  from  use  to  which 
their  apices  and  edges  are  subjected,  to  the  limit  set 
by  the  destructive  effects  of  such  use,  or  by  the  re- 
cuperative energy  of  nutrition. 

5.  The  direction  of  growth  of  the  branches  of  a  V, 
or  of  the  horns  of  a  crescent,  will  be  the  direction  of 
movement  of  the  corresponding  parts  of  the  opposite 
jaw. 

Before  giving  a  review  of  the  various  dental  types 
of  Mammalia,  I  wish  to  describe  some  special  exam- 
ples where  the  effect  of  mechanical  causes  is  most  ob- 
vious. I  therefore  first  repeat  the  observation  of  Ryder 


320    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

as  to  the  origin  of  the  selenodont  molars  of  the  Artio- 
dactyla  ;  and  my  own  as  to  the  origin  of  a  similar 
structure  in  the  molars  of  certain  multituberculate  Pro- 
totheria.  In  the  former  the  mastication  is  ental ;  in 
the  latter  it  is  proal,  as  shown  by  Osborn. 

In  the  accompanying  figure  from  Ryder  the  move- 
ments of  the  lower  jaw  in  mastication  of  lophodonts, 
are  diagrammatically  represented,  a  represents  the 
movement  in  Carnivora,  and  in  the  orthal  bunodonts, 
as  the  pigs,  b  shows  a  slight  lateral  movement  be- 
lieved by  Ryder  to  exist  in  the  wart  hog  (Phacochoa- 


a    t> 

Fig.  88. — Diagram  of  excursion  of  lower  jaw  in  mastication;  from  Ryder; 
a-b,  orthal ;  c-f,  ental. 

rus).  c  represents  the  movement  in  kangaroos,  pha- 
langers,  and  tapirs.  In  d  a  theoretical  intermediate 
movement  is  represented,  such  as  Ryder  supposed  to 
have  characterized  the  Anchitherium.  In  e  the  usual 
movement  among  ruminants  is  depicted,  as  is  seen  in 
the  deer,  etc.  In  /  the  wider  excursion  of  the  jaw  is 
that  seen  in  the  giraffe,  camel,  and  ox.  In  these  move- 
ments from  b  to/,  the  lower  jaw  is  moved  transversely 
across  the  upper  jaw  from  one  side  to  the  other. 
Some  of  the  Diplarthra  masticate  on  one  side  of  the 
jaw  when  performing  this  movement,  and  some  on  the 
other.  That  is,  in  passing  the  lower  jaw  across  the 
face  of  the  upper,  some  masticate  the  food  on  the  side 


KINE  TO  GENESIS. 


321 


where  the  external  face  of  the  lower  jaw  crosses  the 
upper  jaw  from  within  outwards  (ental);  while  in  other 
types  the  food  is  masticated  on  the  side  where  the 
lower  jaw  passes  the  external  edge  of  the  upper  jaw 
from  without  inwards  (ectal).  While  masticating  with 
one  side  of  the  jaws,  the  opposing  dental  series  of  the 
other  side  are  not  in  contact.  All  mutual  effect  of  the 
teeth  of  one  jaw  on  the  other  could  therefore  appear 
on  the  side  temporarily  used  for  mastication  only. 
Among  recent  Un- 
gulata  the  rumi- 
nants present  the 
ental  mastication  ; 
the  rhinoceros  and 
horses,  the  ectal ; 
and  rodents,  the 
proal.  Ryder  is  of 
the  opinion  that  the 
mastication  of  the 
Proboscidia  is  pali- 
nal,  but  I  have  not 
been  able  to  satisfy 
myself  of  this. 

When  the  crests  of  the  inferior  molars  were  devel- 
oped, their  relation  to  the  crests  of  the  superior  molars 
was  always  anterior  in  mastication.  That  is,  the  in- 
ferior crest,  in  the  closing  of  the  jaw,  collides  with  the 
crest  of  the  upper  molar,  with  its  posterior  edge  against 
the  anterior  edge  of  the  latter.  This  is  because  :  first, 
as  to  position,  the  two  anterior  cusps  of  the  lower 
molar  are  the  remains  of  the  anterior  triangle  which 
fit  originally  between  two  superior  molars,  and  be- 
cause, in  the  closing  of  the  jaw,  these  cusps  continue 
to  hold  that  position  ;  and  second,  as  to  function,  be- 


Fig.  89.— Cervus,  molars  :  a,  superior,  exter- 
nal view  ;  b,  do.  inferior  view;  c,  inferior  molars, 
superior  view  ;  from  Ryder. 


322    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

cause  the  canine  in  the  ungulate  series  diminishes  in 
size,  and  does  not,  therefore,  draw  the  inferior  molars 
forwards  by  wedging  on  the  superior  molar,  as  in  the 
Carnivora,  but  allows  free  scope  to  the  posterior  trac- 
tion of  the  temporal  muscle  in  its  exercise  on  the  lower 
jaw. 

In  those  forms  which  masticate  from  the  inside  out- 
wards (the  ental  type),  the  cusps  of  the  inferior  molars, 
passing  between  those  of  the  superior  molars,  would 
tend  to  flatten  the  sides  on  which  they  exerted  fric- 
tion, and  to  extend  those  sides  outwards  beyond  the 
median  apex  of  the  cusp.  (Fig.  90.)  The  result  would 
be,  and  taking  into  view  the  yielding  of  the  tissue  to 


Fig.  90. — Cusps  of  superior  premolars  and  molars  :  «,  external  cusps  of 
molar  of  Sarcothraustes ;  b,  of  Phenacodus  ;  c,  of  Anthracotherium  ;  d,  of 
Oreodon ;  e,  half  of  inferior  molar  of  Cervus;/",  superior  premolar  of  Cory- 
phodon ;  from  Ryder. 

such  strain,  has  been,  to  modify  the  shape  of  the  cusp 
by  pushing  its  side  walls,  so  that  a  horizontal  section 
of  it  would  become  successively  more  and  more  cres- 
centic.  The  effect  on  the  inferior  teeth  would  be  to 
produce  the  same  result  in  their  external  cusps,  but  in 
the  opposite  direction.  The  sides  of  the  cusps  would 
be  pushed  inwards,  past  the  apex,  giving  a  crescentic 
section  more  or  less  perfect,  as  the  operation  of  the 
cause  had  been  of  long  or  short  duration.  The  result 
of  the  lateral  movement  in  mastication  may  be  under- 
stood by  reference  to  the  accompanying  cut,  Fig.  91. 
The  external  crescents  of  the  inferior  molars  (<£)  are 
seen  to  pass  between  the  internal  crescents  of  the 


K1NE  TOGENESIS. 


323 


superior  molars  (a).  The  mutual  interaction  and  effect 
on  the  form  of  the  crescents  may  be  readily  under- 
stood. In  Fig.  90  the  successive  stages  of  this  effect 


Fig.  91  — Two  true  molars  of  both  jaws  of  a  ruminant :  a,  superior  molars, 
their  inner  crescents ;  b,  inferior  molars,  their  external  crescents ;  the  arcs 
show  directions  of  motion  of  jaws  in  mastication;  from  Ryder. 

on  one  or  two  cusps  may  be  seen,  beginning  with  a 
cone  (#)  and  terminating  with  crescents  (ef).  Thus  is 
the  origin  of  the  selenodont  dentition  of  the  highest 


Fig.  92. — Transverse  vertical  sections  of  superior  molar  teeth,  showirg 
transition  from  bunodont  (A)  type  to  lophodonts  (B,  C).  A,  Sus  erymanthius. 
B,  Ovis  amaltheus.  C,  Bos  taurus.  From  Gaudry.  Letters  :  d,  dentine  ;  e, 
enamel ;  c,  cementum. 

artiodactyle  explained  by  Ryder,  and,  I  believe,  cor- 
rectly. 

Kowalevsky  and  I  have  shown  that  the  types  with 
selenodont  (crescent-bearing)  molars,  have  descended 


324    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

from  tubercle-bearing  (bunodont)  ancestors.  This  de- 
scent has  witnessed  an  increased  depth  of  the  infold- 
ing of  the  crown,  as  represented  in  the  accompanying 
figure.  Now,  in  the  table  of  masticatory  types  above 
given  it  is  shown  that  in  the  bunodont  type  of  the 
Suoidea  the  mastication  is  orthal,  and  a  gradual  in- 
crease in  the  length  of  the  lateral  excursions  of  the 
lower  jaw  has  been  shown  to  have  resulted  in  the  ental 
mastication.  Thus  has  structure  kept  pace  with  func- 
tion in  the  evolution  of  the  selenodont  dentition. 


Fig.  93.—  Chirox plicatus  Cope,  palate  and  molar  teeth  from  below,  three- 
halves  natural  size.  From  Puerco  bed  of  New  Mexico.  From  American  Nat- 
uralist, 1887,  p.  566. 

The  general  structure  of  the  dentition  in  the  Proto- 
theria  Multituberculata  is  similar  to  that  of  the  Glires. 
The  incisors  in  the  Plagiaulacidae,  Chirogidae,  and  Poly- 
mastodontidae  have  structure  and  functions  generally 
similar  to  those  of  that  order.  The  result  in  the 
form  and  function  of  the  molar  dentition  has  been  sim- 
ilar to  that  observed  in  the  Glires.  The  postglenoid 
process  is  probably  absent  in  these  animals  ;  in  any 
case  the  mandibular  condyle  is  rounded,  and  is  not 
transverse.  Prof.  H.  F.  Osborn  has  pointed  out  to 
me  that  mastication  was  performed  by  a  fore-and-aft 


K1NE  TO  GENESIS.  325 

movement  of  the  inferior  molars  on  the  superior  in 
Plagiaulacidae.  This  was  no  doubt  the  case  in  the 
oth^r  families  named.  The  molar  teeth  of  the  lower 
types,  as  Tritylodon  from  the  Trias,  present  conical 
tubercles  in  longitudinal  series,  two  in  the  lower  and 
three  in  the  upper  jaw.  The  two  series  of  the  lower 
jaw  alternate  with  the  three  in  the  upper  jaw,  moving 
in  the  grooves  between  the  latter,  while  the  three  se- 
ries of  the  upper  molars  reciprocally  embrace  the  two 
of  the  lower  molars.  This  is  demonstrated  by  the 
mutual  wear  of  the  tubercles 
seen  in  Ptilodus  and  Chirox 
(Fig.  93).  The  trituration 
was  probably  the  same  in  Tri- 
tylodon, but  in  Polymastodon 
the  increased  thickening  of 
the  tubercles  prevented  their 
interlocking  action  in  masti- 
cation. In  this  genus  the  tu- 
bercles Slid  OVer  each  Other,  f\^.g^.— A,  Meniscoessus conquis- 

and    truncated     the    apices  ^  cope,  last  two  superior  molars. 

from    the    Laramie    of   Wyoming, 
Until    in    Old    Specimens    they    twice  natural  size.    B,  Meniscoessus, 

were  entirely  worn  away.  In  second  species' from  Osborn' 
Meniscoessus  (Fig.  94)  and  Stereognathus  we  have  an 
interesting  illustration  of  the  effect  of  the  action  of 
cusps  on  each  other  when  under  prolonged  mutual 
lateral  thrust.  Their  external  sides  have  been  drawn 
out  into  angles  in  the  direction  of  thrust,  converting 
their  transverse  sections  from  circles  to  crescents.  As 
the  thrust  is  in  the  Multituberculata  longitudinal,  the 
crescents  are  transverse  to  the  axis  of  the  jaw.  In  the 
selenodont  Artiodactyla,  where  the  thrust  is  transverse 
to  the  line  of  the  jaw,  the  crescents  are  longitudinal. 
That  similar  effects  should  accompany  similar  move- 


326    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

ments  in  two  groups  of  Mammalia  so  widely  separated 
as  these  two  is  strong  evidence  in  favor  of  the  belief 
that  the  two  facts  stand  in  the  relation  of  cause  and 
effect. 

I  now  present  an  example  of  the  effect  of  strain,  as 
shown  by  the  direction  of  the  inferior  incisors  of  the 
lemurine  Quadrumana.  These  teeth  project  horizon- 
tally from  the  extremity  of  the  mandible,  so  as  not  to 
oppose  the  superior  incisors,  in  consequence  of  which 
they  are  useless  as  organs  of  prehension.  But  they 


Fig-  95- — Lemur  collaris,  dentition  from  below  and  above  ;  natural  size ; 
original. 

are  used  by  their  possessors  as  a  comb  for  the  fur, 
drawing  them  from  below  upwards  when  thus  employ- 
ing them.  The  strain  is  always  in  one  direction,  and 
must  have  resulted  in  developing  the  procumbent  posi- 
tion which  they  now  display  (Fig.  95).  This  is  a  di- 
rect deduction  from  the  fact  that  the  incisor  teeth  are 
similarly  displaced  by  the  pressure  of  the  tongue  in 
cases  of  the  abnormal  enlargement  of  that  organ  in 
man. 

I  now  describe  the  general  character  of  mammalian 
dentition,  with  the  view  of  pointing  out  how  strong,  in 


KINETOGENESIS.  327 

the  light  of  the  facts  already  cited,  is  the  evidence  of 
their  origin  through  mechanical  strains  and  impacts. 

a.    The  Origin  of  Canine  Teeth. 

The  origin  of  canine,  pseudo-canine,  and  canine- 
like  incisor  teeth  is  due  to  the  strains  sustained  by 
them  on  account  of  their  position  in  the  jaws  at  points 
which  are  naturally  utilized  in  the  seizing  of  prey,  or 
the  fighting  of  enemies.  In  some  reptiles  (Dimetro- 
don)  the  end  of  the  muzzle  has  been  utilized  ;  in  croco- 
diles, the  side  of  the  jaw ;  while  the  intermediate 
position  has  been  most  used  by  Mammalia.  The  rea- 
son why  the  canine  instead  of  the  incisor  teeth  have 
been  selected  by  carnivorous  Mammalia  for  prehensile 
purposes  is  not  at  present  clear  to  me.  In  accordance 
with  Rule  I.,  its  increased  size  has  been  due  to  the 
especial  and  energetic  strains  to  which  it  has  been 
subjected  while  in  use  as  a  prehensile  or  offensive 
weapon,  when  buried  in  the  body  of  its  prey  or  enemy. 
The  superior  canine  would  acquire  larger  size  earlier 
in  time  than  the  inferior  canine,  since  it  bears  the 
greater  part  of  such  strain,  as  attached  to  the  more 
fixed  head  and  body  of  its  possessor.  The  anterior 
teeth  of  the  lower  jaw  would  be  less  available  for  use, 
since  they  offer  weaker  and  less  fixed  resistance  to  the 
opposing  body.  That  the  first  tooth  behind  the  canine 
was  not  generally  enlarged  is  (under  I.)  due  to  the 
fact  that  its  posterior  position  prevents  it  from  having 
the  same  amount  of  use,  and  experiencing  the  strain 
that  a  tooth  more  anteriorly  placed  necessarily  re- 
ceives. It  is  excluded  from  considerable  use  by  the 
projecting  muzzle  above  and  in  front  of  it.  That  it 
was  not  drawn  out  into  a  horizontal  position  was  due 
to  the  presence  of  teeth  anterior  to  it. 


328    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


That  the  increased  size  of  canine  teeth  is  due  to 
strains  is  strongly  indicated  by  the  huge  development 
of  these  teeth  in  the  walrus.  This  animal  uses  its  ca- 
nines for  the  breaking  of  ice,  and  for  lifting  itself  from 
the  water  on  to  the  edge  of  strong  ice.  The  fact  that 
canines  and  not  incisors  have  been  thus  developed  is 
a  necessary  result  of  the  fact  that  the  walrus  is  a  de- 
scendant of  a  line  of  animals  which  had  already  re- 
duced "incisors  and  larger  canines. 

b 


Fig.  96. — Esthonyx  burmeisterii  Cope,  dentition:  «,  profile;  b,  superior; 
c,  inferior  dentition,  grinding  faces.  Reduced. 

b.   Development  of  the  Incisors. 

The  history  of  the  incisor  teeth  of  the  Mammalia 
exhibits  three  processes,  viz. :  hypertrophy  (e.  g. 
Glires),  specialization  (e.  g.  Galeopithecus,  Lemur- 
idae),  and  atrophy  (e.  g.  Booidea,  Phacochcerus,  Glos- 
sophaga,  etc.). 


KINE  TOGENESIS. 


329 


Of  hypertrophy  we  have  two  types  :  the  first  repre- 
sented by  the  Glires,  Multituberculata,  Tillodonta  and 
their  ancestors;  and  second,  by  the  Proboscidia,  the 
narwhal  and  certain  Sirenia.  As  the  uses  of  the  inci- 
sors present  two  types  corresponding  with  their  struc- 
ture, we  have  ground  for  believing  the  uses  in  question 
to  have  been  the  efficient  agent  in  producing  the  lat- 
ter. Esthonyx  furnishes  us  with  an  example  (Fig.  96) 
where  all  the  incisors  are  present  in  the  lower  jaw,  and 


a 


Fig.  yj.—Psittacotherium  multifragum  Cope,  mandibular  ramus,  one-half 
natural  size  ;  a,  profile ;  b,  from  above. 

where  the  function  of  one  pair  of  them  (the  second) 
has  evidently  been  partially  rodent  in  character;  that 
is,  it  has  served  as  a  scraper  and  gouger  of  food  sub- 
stances. Persistent  use  has  apparently  developed  the 
size  of  this  pair  of  teeth,  until  we  find  in  Psittacothe- 
rium  (Fig.  97)  they  have  reached  a  greater  efficiency, 
and  that  the  external  incisors  of  the  lower  jaw  have 
disappeared.  This  disappearance  can  be  accounted 
for  on  the  ground  of  disuse,  a  retirement  from  service 
due  to  position,  and  the  increased  growth  of  incisor 


330    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

No.  2.  In  Calamodon  the  first  incisor  has  become  ru- 
dimentary from  the  same  cause,  and  in  Anchippodus 
it  has  disappeared  altogether,  leaving  a  truly  rodent 
incisor  dentition,  consisting  of  the  second  incisors 
only,  in  the  lower  jaw.  Continued  use  as  chisels  has 
developed  these  teeth  to  the  great  proportions  seen 
in  such  Glires  as  Castoroides,  etc.  (Fig.  107). 

The  use  which  the  Proboscidia  and  Sirenia  (Hali- 
core)  give  their  incisors,  is,  from  a  mechanical  point 
of  view,  like  that  which  the  Carnivora  give  their  ca- 
nines ;  that  is,  it  consists  of  impacts  in  the  long  axis, 
and  strains  transverse  to  the  long  axis  of  the  tooth. 
The  elephants  use  their  tusks  for  prying  up  the  vege- 
tables on  which  they  feed,  or  for  pushing  aside  the 
vegetation  through  which  they  wish  to  pass.  The  an- 
cestors of  the  Proboscidia  are  not  certainly  known, 
but  they  possessed  incisors  of  enlarged  proportions, 
such  as  we  find  in  the  Toxodontia  and  other  late  rep- 
resentatives of  some  of  the  primitive  Ungulata.  Use 
of  such  teeth  in  the  manner  referred  to,  without  oppo- 
sition from  the  inferior  incisors,  will  account  for  the 
tremendous  proportions  which  they  ultimately  reached 
in  some  of  the  species  of  Elephas. 

The  use  made  by  the  narwhal  of  its  single  huge 
superior  incisor,  that  of  an  ice-breaker,  indicates  the 
origin  of  its  large  dimensions.  So  with  the  straight 
incisors  of  the  hippopotamus;  use  as  diggers  has 
straightened  them  to  a  horizontal  from  their  primitive 
vertical  direction,  a  change  which  is  also  partially  ac- 
complished in  the  true  pigs  (Sus). 

In  the  Sirenian  genus  Halicore  the  upper  incisors 
have  been  used  in  excavating  vegetable  growths  from 
the  banks  and  bottom  of  shallow  seas.  The  transition 
from  three  incisors  (Prorastomus)  to  two  (Dioplothe- 


KINETOGENESIS.  331 

rium),  and  to  one  (Halicore),  is  identical  with  what 
has  taken  place  in  the  Proboscidia  and  Glires,  and 
has  resulted  in  the  production  of  an  effective  digging- 
tool.  In  other  genera  it  ma)'  be  supposed  that  their 
habits  of  browsing  on  soft  growing  materials  did  not 
necessitate  the  use  of  digging  incisors,  hence  these 
teeth  became  atrophied,  as  in  the  manatee  and  Rhy- 

tina. 

c.   Development  of  Molars. 

In  fishes  and  reptiles  where  teeth  occasionally  pre- 
sent very  primitive  conditions,  the  theory  of  the  origin 
of  particular  types  of  molar  teeth  is  more  simple  than 
in  the  case  of  Mammalia.  The  observations  of  Hiiter 
on  the  action  of  osteoblasts  under  stimulus  show  that 
under  moderate  irritation  osseous  tissue  is  deposited, 
while  under  severe  pressure  osseous  tissue  is  removed. 
Koelliker  has  shown  that  the  action  of  these  bodies  is 
the  same  in  dentine  as  in  true  bone.  Hence  modifica- 
tions of  dental  structure  must  stand  in  close  relation  to 
the  uses  to  which  they  are  put.  Thus  severe  pressure 
on  a  simple  tooth  crown  would,  if  long  continued,  cause 
it  to  expand  laterally,  or  in  the  direction  of  least  re- 
sistance, and  to  grow  but  little  in  its  vertical  axis,  i.  e., 
in  the  direction  of  greatest  resistance.  The  molar 
teeth  have  been  subjected  to  much  more  severe  direct 
irritation  from  use  than  any  others  in  the  jaws,  and 
this  will  account  for  their  increased  diameters. 

In  the  case  of  the  eutherian  Mammalia,  molar  teeth 
are  not  traceable  back  to  ancestral  types  of  reptilian  mo- 
lars, but  to  simple  conic  (haplodont)  reptilian  teeth. 
The  process  of  the  evolution  of  the  complex  mamma- 
lian molars  from  these,  forms  the  subject  of  a  paper  in 
the  American  Journal  of  Morphology  for  1889,  from  which 
I  quote  extensively  in  the  present  work. 


332    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

I  have  there  shown  that  the  greater  number  of  the 
types  of  this  series  have  derived  the  characters  of  their 
molar  teeth  from  the  stages  of  the  following  succes- 
sion. First  a  simple  cone  or  reptilian  crown,  alternat- 
ing with  that  of  the  other  jaw  (haplodont  type).  Sec- 
ond, a  cone  with  lateral  denticles  (the  triconodont 
type).  Third,  the  denticles  to  the  inner  or  outer  side 
of  the  crown,  forming  a  three-sided  prism,  with  tritu- 
bercular  apex,  which  alternates  with  that  of  the  oppo- 
site jaw  (tritubercular  type).  Fourth,  development  of 
a  heel  projecting  from  the  posterior  base  of  the  lower 
jaw,  which  meets  the  crown  of  the  superior,  forming  a 
tuberculosectorial  inferior  molar.  From  this  stage 
the  carnivorous  and  sectorial  dentition  is  derived,  the 
tritubercular  type  being  retained.  Fifth,  the  develop- 
ment of  a  posterior  inner  cusp  of  the  superior  molar 
and  the  elevation  of  the  heel  of  the  inferior  molar, 
with  the  loss  of  the  anterior  inner  cusp.  Thus  the 
molars  become  quadritubercular,  and  opposite.  This 
is  the  type  of  many  of  the  Taxeopoda,  including  the 
Quadrumana  and  Insectivora  as  well  as  the  inferior 
Diplarthra.  The  higher  Taxeopoda  (Hyracoidea)  and 
Diplarthra,  add  various  complexities.  Thus  the  tu- 
bercles become  flattened  and  then  concave,  so  as  to 
form  V's  in  the  section  produced  by  wearing  ;  or  they 
are  joined  by  cross-folds,  forming  various  patterns.  In 
the  Proboscidia  the  latter  become  multiplied  so  as  to 
produce  numerous  cross-crests. 

d.    Origin  of  the  Carnivorous  Dentition. 

The  anterior  cusplet  of  the  triconodont  crown  is 
(Fig.  98  A),  in  the  upper  jaw,  the  paracone,  and  in  the 
lower  jaw  the  paraconid  ;  and  the  posterior  cusplet  is 
the  metacone  or  metaconid,  respectively.  As  the  prin- 


KINETOGENESIS.  333 

cipal  cusps,  or  protocone  and  protoconid,  alternate  with 
each  other,  the  cusplets  stand  opposite  to  them  in  the 
closing  of  the  jaws,  and  a  certain  amount  of  interfer- 
ence results.  As  the  lesser  cusps  are  the  less  resistant 
to  the  wedging  press'ure  of  such  contact,  their  position 
would  change  under  its  influence,  rather  than  the  large 
central  cusps.  The  lower  jaw  fitting  within  the  upper, 
the  effect  of  the  collision  between  the  major  cusps  of 
the  one  jaw,  and  cusplets  of  the  other,  would  be  to 
emphasize  the  relation  still  more  ;  that  is,  the  cusplets 
of  the  upper  jaw  would  be  wedged  outwards,  while 
those  of  the  lower  jaw  would  be  pressed  inwards,  the 
major  cusps  retaining  at  first  their  original  alternate 
position.  With  increase  of  the  size  of  the  teeth  the 
cusps  would  soon  assume  in  each  jaw  a  position  more 
or  less  transverse  to  that  of  the  other  jaw,  producing, 
as  a  result  of  the  crowding,  a  crown  with  a  triangular 
section  in  both.  The  process  may  be  rendered  clear 
by  the  following  diagram  : 


B  C 

Fig.  98. — Diagrammatic  representations  of  horizontal  sections  of  tricuspi- 
date  molars  of  both  jaws  in  mutual  relation  ;  the  shaded  ones  represent  those 
of  the  upper  jaw:  A,  Triconodon  ;  B,  Menacodon  ;  C,  ideal  tritubercular  mo- 
lars, approached  by  Menacodon,  B. 

It  is  supposed  on  the  contrary  by  Rose  and  Kiiken- 
thal  that  mammalian  molars  which  support  more  than 
one  cusp  have  been  formed  by  the  fusion  of  several 
simple  reptilian  cones.  So  far  as  regards  the  higher 
Mammalia  this  hypothesis  is  in  opposition  to  all  the 
facts  of  paleontology  and  is  not  worthy  of  discussion. 


334    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

The  only  question  that  can  arise  is  with  reference  to 
the  origin  of  the  multituberculate  molar  of  the  Proto- 
theria. 

It  is  further  questioned  by  Forsyth- Major,  whether 
the  tritubercular  molar  has  been  derived  from  the  tri- 
conodont.  He  believes,  on  the  contrary,  that  it  is  de- 
rived from  the  multitubercular  type  by  reduction. 
There  are  two  objections  to  this  view  :  (i)  the  cones 
of  the  tritubercular  tooth  or  trigon  should  be  subequal, 
were  they  derived  from  a  multitubercular  source.  On 
the  contrary,  the  two  external  cones  of  the  upper,  and 
the  two  inner  cones  of  the  lower  series  are  in  the 
earliest  (Jurassic),  as  well  as  most  of  the  tritubercular 
types,  smaller  than  the  single  opposite  cusp  or  proto- 
cone,  precisely  as  are  the  anterior  and  posterior  cones 
of  the  triconodont  molar.  (2)  No  paleontologic  series 
from  the  multitubercular  to  the  tritubercular  types  has 
been  traced,  while  the  series  from  the  triconodont  to 
the  tritubercular  is  well  known.  Forsyth-Major's  evi- 
dence that  such  a  transition  exists  in  the  Glires,  is 
better  explained  by  tracing  the  moderate  complexity 
he  describes  to  a  tritubercular  origin. 

It  is  also  alleged  by  Allen  and  Scott  that  the  inter- 
nal cusps  of  the  premolars,  when  present,  originate  by 
the  development  of  internal  cingula,  and  have  no  prim- 
itive tritubercular  ancestry.  The  evidence  at  our  dis- 
posal from  paleontological  sources  is  in  favor  of  this 
view;  hence  it  is  reasoned  that  the  history  of  the  mo- 
lar teeth  must  have  been  identical.  This  however  does 
not  follow,  especially  as  the  paleontologic  evidence 
points  the  other  way.  The  history  of  the  two  series 
has  been  different.  In  the  first  place  the  premolars 
have  been  subjected  to  much  less  use  than  the  true 
molars ;  hence  they  retained  the  primitive  reptilian 


KINETOGENESIS.  335 

simplicity  for  a  much  longer  period,  a  simplicity  which 
they  retain  in  the  Carnivora,  except  the  J-,  which  be- 
came the  sectorial.  Secondly,  the  premolars,  instead 
of  increasing  in  size,  have  in  many  types  decreased  ; 
the  Diplarthra  alone  presenting  an  exception  to  this 
rule.  That  the  internal  cusps  of  the  premolars  may 
have  arisen  by  growth  of  cingula  in  this  order,  is  by  no 
means  improbable.  We  seem  to  have  here  an  excel- 
lent illustration  of  the  origin  of  two  identical  struc- 
tures by  different  evolutionary  routes. 

The  first  modification  of  the  tritubercular  molar  of 
the  lower  jaw  is  the  addition  of  a  low  cingulum  at  the 
posterior  base.  This  is  seen  in  a  rudimentary  condi- 
tion in  various  living  species  of  the  Centetidae  and 
Chrysochloridse  of  the  insectivorous  order  (Fig.  100); 
but  in  these  existing  forms  the  superior  molar  has 
added  a  posterior  cingulum  also,  which  widens  inter- 
nally, or  towards  the  palate  (Fig.  101).  In  the  evolu- 
tion of  the  dentition,  the  inferior  posterior  cingulum, 
or  " heel, "was  developed  first,  as  in  the  Deltatherium, 
Centetes,  and  Stypolophus  (Figs.  99,  100,  102),  where 
it  is  quite  large ;  while  the  superior  cingulum  is  want- 
ing in  Stypolophus  and  Didelphodus,  but  is  present  in 
a  very  rudimentary  condition  in  Deltatherium  fundami- 
nis.  In  all  of  these  genera  the  external  cusps  of  the 
superior  series  have  been  pressed  inwards,  and  more 
or  less  together,  and  are  therefore  removed  in  this  re- 
spect from  the  primitive  condition.  The  more  primi- 
tive state  of  the  superior  cusps  is  seen  in  some  species 
of  Mioclaenus,  where,  however,  a  posterior  cingulum 
may  be  developed.  The  primitive  type  of  tritubercular 
superior  molar  is  that  of  Sarcothraustes,  and  in  the 
same  genus  the  inferior  molar  only  differs  from  the 
primitive  type  in  having  a  well-developed  heel.  Among 


336   PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

recent  Mammalia  the  carnivorous  and  insectivorous 
Marsupialia  generally  have  the  tritubercular  lower  mo- 
lar with  heel.  In  the  Chiroptera  and  many  Insectivora 
the  heel  is  largely  developed,  and  supports  two  cusps, 
as  it  does  in  some  Creodonta. 


-  99- — Deltatherium  fundaminis  Cope,  fragmentary  skull,  two-thirds 
natural  size  ;  from  the  Puerco  bed  of  New  Mexico.  a,b,  c,  from  one  individ- 
ual;  d,  from  a  second  animal;  a,  right  side  of  cranium;  b,  palate  from  be- 
low ;  c,  mandible,  part  from  above ;  d,  left  ramus,  outer  side ;  from  the  Re- 
port of  the  U.  S.  Geol.  Surv.  Terrs.,  Vol.  III. 

From  this  point  the  evolution  of  the  tritubercular 
molar  must  be  considered  from  two  standpoints.  The 
first  is  the  mechanical  cause  of  the  changes  of  its  form  ; 
and  the  second  is  the  mechanical  cause  of  its  definite 


KINE  TOGENESIS. 


337 


location  in  a  particular  part  of  the  jaw.  For  it  has 
been  already  stated  that  in  the  evolution  of  the  secto- 
rial  dentition  of  the  Carnivora,  the  number  of  molars 
and  premolars  has  considerably  diminished,  while 
those  that  remain  have  become  relatively  much  larger. 
In  the  tritubercular  dentition  the  crowns  proper  of 
one  jaw  alternate  with  those  of  the  other  (Fig.  100); 
but  when  heels  are  added  in  either  jaw,  they  will  op- 
pose such  part  of  the  crowns  of  the  teeth  in  the  oppo- 


Fig.  loo.—Centetes  ecaudatus:  A,  skull,  side  seen  obliquely  from  below; 
B,  superior  molars  from  below  ;  C,  inferior  molars  from  above. 

site  jaw  as  comes  in  contact  with  them  when  in  use. 
The  development  of  the  heel  in  the  inferior  molars 
produced  a  type  which  is  known  as  the  tuberculosec- 
torial.  This  type  characterizes  the  Creodonta  and  a 
few  Carnivora.  In  the  former  there  are  generally 
three  such  teeth,  in  the  latter  but  one. 

In  the  tuberculosectorial  type  of  inferior  molar  the 
primitive  tritubercular  part  of  the  crown  (trigonid  of 
Osborn)  stands  principally  anterior  to  the  posterior 


338    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

root  of  the  tooth.  It  appears  that  the  posterior  root 
has  been  extended  backwards,  so  as  to  occupy  a  posi- 
tion below  the  middle  of  the  superior  molar,  while  the 
tritubercular  crown  has  been  confined  to  the  space  be- 
tween the  crowns  of  the  superior  molars.  This  would 
follow  of  necessity  from  the  alternating  action  of  the 
crowns  of  the  opposite  series,  in  connection  with  a 
general  increase  in  size  of  the  teeth.  In  the  opening  of 


,/»<?< 


Fig.  loi.— Series  of  inferior  molar  crowns  representing  the  transition  from 
the  simple  (haplodont)  to  the  quadritubercular.     From  Osborn. 

the  jaws  in  a  Creodont,  the  elevated  portion  of  the  in- 
ferior crown  shears  by  its  posterior  face  against  the 
anterior  face  of  the  superior  molar,  thus  restraining  its 
extension  posteriorly.  The  stimulus  of  use,  however, 
develops  a  low  extension  posteriorly,  or  a  heel,  which 
covers  the  posterior  root,  and  opposes  in  mastication 
the  internal  extremity  or  tubercle  of  the  crown  of  the 
superior  molar  above  it.  Thus  a  molar  element  in 


KINETOGENESIS.  339 

mastication  is  added  to  the  sectorial  in  some  Creodonta, 
and  in  CanidaB  and  Ursidae,  etc.,  among  Carnivora. 
This  function  predominates  over  that  of  the  anterior 
triangle  in  the  Lemuridae.  (Fig.  95.) 

I  have  already  pointed  out  the  successive  modifica- 
tions of  form  which  have  resulted  in  the  existing  spe- 
cialized single  inferior  sectorial  tooth  of  the  Felidae. 
They  consist  in  the  gradual  obliteration  of  the  poster- 
ior-internal cusp,  and  of  the  heel,  and  the  enlargement 
of  the  external  and  anterior  internal  tubercles  of  the 
primitive  triangle.  The  modification  in  the  character 
of  the  dentition  taken  as  a  whole  was  shown  to  consist 


Fig.  \vz.-Stypholophus  whztite  Cope  ;  diagram  representing  the  apposition 
of  the  inferior  and  superior  molars.  The  superior  are  in  light,  the  inferior 
in  heavy  lines.  The  numbers  represent  the  molars  and  premolars  :  C,  canine; 
poc,  protocone;  pac,  paracone;  me,  metacone;  POC,  protoconid;  PAC,  para- 
conid  ;  MC,  metaconid  ;  he,  hypocone  ;  HC,  hypoconid. 

in  the  reduction  of  the  number  of  the  teeth,  including 
the  sectorials,  until  in  Felis,  etc.,  we  have  almost  the 
entire  function  of  the  molar  series  confined  to  a  single 
large  sectorial  in  each  jaw. 

The  genesis  of  the  superior  sectorial  tooth  has 
been  explained  as  follows.  In  consequence  of  the 
fact  that  the  lower  canine  tooth  shuts  anterior  to  the 
superior  canine,  the  result  of  the  enlargement  of  the 
diameters  of  those  teeth  will  be  to  cause  the  crowns 
of  the  inferior  teeth  to  be  drawn  from  behind  forwards 
against  those  of  the  superior  teeth  when  the  jaw  is 
closed  (Fig.  102).  Thus  a  shearing  motion  would  re- 


34o    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

suit  between  the  anterior  external  edge  of  the  lower 
triangle  and  the  posterior  internal  edge  of  the  superior 
triangle.  Now  the  characters  of  the  true  sectorial  teeth 
consist  in  the  enormous  extension  of  these  same  edges 
in  a  fore  and  aft  direction,  the  inferior  shutting  inside 
of  the  superior.  To  account  for  the  development  of 
these  blades  we  must  understand  that  the  oblique  pres- 
sure of  the  front  edge  of  the  lower  tooth,  on  the  hind 
edge  of  the  superior  tooth,  has  been  continued  for  a 
very  long  time.  We  must  then  observe  that  the  inter- 
nal tubercle  of  the  superior  triangle  has  been  pushed 
continually  forwards  and  been  reduced  to  a  very  small 
size.  Why  should  this  occur?  Why  should  not  the 
corresponding  tubercles  of  the  inner  side  of  the  lower 
crown  have  been  pushed  backwards,  since  action  and 
reaction  are  equal  ?  The  reason  is  clear  :  The  superior 
tubercle  is  on  the  internal  apex  of  the  trigon,  and  is 
supported  by  but  one  root,  while  the  resistant  portion 
of  the  inferior  crown  is  the  base  of  the  trigonid,  and 
is  supported  by  two,  thus  offering  twice  the  resistance 
to  the  pressure  that  the  superior  does.  But  why  should 
the  anterior  part  of  the  inferior  tooth  move  forwards? 
even  if  it  be  in  the  direction  of  least  resistance?  This 
is  due  to  the  regular  increase  in  size  of  the  teeth  them- 
selves, an  increase  which  can  be  traced  from  the  be- 
ginning to  the  end  of  the  series.  And  this  increase  is 
the  usual  result  of  use  (Fig.  102). 

The  mechanics  of  the  above  proposition  I  believe 
to  be  correct,  but  I  have  had  occasion  to  modify  the 
statement  as  to  the  initiatory  cause  of  the  process.  In 
many  primitive  Ungulata  the  canines  have  been  as 
well  developed  as  in  the  Carnivora,  yet  the  forward 
pressure  of  the  inferior  molars  on  the  superiors  has 
not  resulted,  or  has  not  been  sufficient  to  produce  sec- 


KINETOGENESIS.  341 

torial  molars  in  those  types.  In  the  Amblypoda,  the 
lower  molars  even  shear  backwards  on  the  upper  ones. 
It  seems  then  that  this  growth  of  the  canines  is  not  in 
all  instances  sufficient  to  cause  a  proterotome  masti- 
cation. I  suspect  that  the  more  usual  cause  is  to  be 
found  in  the  voluntary  effort  of  the  primitive  flesh- 
eater,  to  masticate  flesh  by  the  manipulation  of  his 
lower  jaw  and  the  body  to  be  divided.  The  presence 
of  the  inferior  canine  forbids  a  posterior  shearing  move- 
ment of  the  molars,  so  that  the  anterior  shear  is  the 
only  one  possible  to  most  of  the  Creodonta.  The  ab- 


Fig.  103. — Cynodictis  geismarianus  Cope ;  skull   one-half  natural  size :  a, 
right  side;  b,  left  side  from  below. 

sence  of  preglenoid  crest  in  primitive  Creodonta  will 
permit  a  manipulation  such  as  we  observe  in  various 
ungulates  to-day.  The  formation  of  a  habit  of  a  pro- 
terotome mastication  would  result,  and  the  structural 
results  would  succeed  as  above  pointed  out. 

The  excess  of  the  forwards  pressure  of  the  inferior 
teeth  against  the  superior  over  any  backwards  pres- 
sure, has  left  the  posterior  internal  cusp  of  the  triangle 
of  the  inferior  molar  (metaconid)  without  contact  or 
consequent  functional  use.  It  has,  consequently,  grad- 
ually disappeared,  having  become  small  in  the  highest 


342    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

Canidae,  and  wanting  in  some  Mustelidae,  and  all  Fe- 
lidae.  The  heel  of  the  same  tooth  has  had  a  similar 
history.  With  the  diminution  in  size  of  the  first  supe- 
rior tubercular,  with  which  it  comes  in  opposition  in 
mastication,  its  functional  stimulus  also  diminished ; 
and  it  disappeared  sometimes  a  little  sooner  (Felidae) 
and  sometimes  a  little  later  (Hyaenidae")  than  that  tooth. 
The  specialization  of  one  tooth  to  the  exclusion  of 
others  as  a  sectorial,  appears  to  be  due  to  the  follow- 
ing causes.  It  is  to  be  observed  in  the  first  place  that 
when  a  carnivore  devours  a  carcass,  it  cuts  off  masses 
with  its  sectorials,  using  them  as  shears.  In  so  doing 


«         *        3  i. 

Fig.  \v\.—Aelurodon  seevus  Leidy ;  diagram  representing  coadaptation  of 
crowns  of  superior  and  inferior  molars  in  mastication  ;  lines  and  lettering  as 
in  Fig.  102. 

it  brings  the  part  to  be  divided  to  the  angle  or  canthus 
of  the  soft  walls  of  the  mouth,  which  is  at  the  front  of 
the  masseter  muscle.  At  this  point  the  greatest  amount 
of  force  is  gained,  since  the  weight  is  thus  brought 
immediately  to  the  power,  which  would  not  be  the  case 
were  the  sectorial  situated  much  in  front  of  the  mas- 
seter. On  the  other  hand,  the  sectorial  could  not  be 
situated  farther  back,  since  it  would  then  be  inacces- 
sible to  a  carcass  or  mass  too  large  to  be  taken  into 
the  mouth. 

The  position  of  the  sectorial  tooth  being  thus  shown 
to  be  dependent  on  that  of  the  masseter  muscle,  it  re- 
mains to  ascertain  a  probable  cause  for  the  relation  of 


KINETOGENESIS.  343 

the  latter  to  the  dental  series  in  modern  Carnivora. 
Why,  for  instance,  were  not  the  last  molars  modified 
into  sectorial  teeth  in  these  animals,  as  in  the  extinct 
Hyaenodon,  and  various  Creodonta.  The  answer  ob- 
viously is  to  be  found  in  the  development  of  the  pre- 
hensile character  of  the  canine  teeth.  It  is  probable 
that  the  gape  of  the  mouth  in  the  Hyaenodons  was 
very  wide,  since  the  masseter  was  situated  relatively 
far  posteriorly.  In  such  an  animal  the  anterior  parts 
of  the  jaws  with  the  canines  had  little  prehensile  power, 
as  their  form  and  anterior  direction  also  indicates. 
They  doubtless  snapped  rather  than  lacerated  their 
enemies.  The  same  habit  is  seen  in  the  existing  dogs, 
whose  long  jaws  do  not  permit  the  lacerating  power 
of  the  canines  of  the  Felidae,  though  more  effective  in 
this  respect  than  those  of  the  Hyaenodons.  The  use- 
fulness of  a  lever  of  the  third  kind  depends  on  the  ap- 
proximation of  the  power  to  the  weight ;  that  is,  in  the 
present  case,  the  more  anterior  the  position  of  the 
masseter  muscle,  the  more  effective  the  canine  teeth. 
Hence  it  appears  that  the  relation  of  this  muscle  to 
the  inferior  dental  series  depended  originally  on  the 
use  of  the  canines  as  prehensile  and  lacerating  organs, 
and  that  its  relative  insertion  has  advanced  from  be- 
hind forwards  in  the  history  of  carnivorous  types. 
Thus  it  is  that  the  only  accessible  molars,  the  fourth 
above  and  the  fifth  below,  have  become  specialised  as 
sectorials,  while  the  fifth,  sixth,  and  seventh  have, 
firstly,  remained  tubercular  as  in  the  dogs,  or,  sec- 
ondly, have  been  lost,  as  in  hyaenas  and  cats. 

The  reduction  of  the  number  of  molars  in  relation 
to  the  increase  in  the  size  of  the  canines  commenced 
as  early  as  the  Jurassic  period.  It  is  seen  in  the  gen- 
era Triconodon  (Owen)  and  Paurodon  (Marsh),  where 


344    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


KINE  TO  GENESIS. 


345 


the  canines  are  large  and  the  molars  few.  In  the 
Plagiaulacidae  a  similar  relation  is  seen  between  the 
development  of  the  incisors  and  the  reduction  in  num- 
ber of  the  molars.  This  is  the  modification  of  relation 


observed  in  existing  Mammalia  of  the  orders  Probos- 
cidia  and  Glires,  which  will  be  mentioned  later,  under 
the  head  of  proal  dentition. 

e.    Origin  of  the  Dental  Type  of  the  Glires. 

The  peculiarities  of  the  rodent  dentition  consist,  as  is 
well  known,  in  the  great  development  of  the  incisors ; 


346    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

the  loss  of  the  canine  and  of  all  but  one,  or  rarely  of 
two,  of  the  premolars,  which  leave  a  wide  diastema ; 
and  the  posterior  position  of  the  molar  teeth,  as  relates 
to  the  rest  of  the  skull.  A  peculiarity  which  belongs  to 
the  highest  types  of  the  order  is  the  prismatic  form  of 
the  molars,  and  the  deep  inflection  of  their  always 
transverse  enamel  folds  both  laterally  and  vertically. 
A  peculiarity  of  the  masticating  apparatus,  which  is  the 
basis  of  distinction  from  the  bunotherian  order,  is  the 
lack  of  postglenoid  process,  and  the  consequent  freedom 
of  the  lower  jaw  to  slide  backwards  and  forwards  in 
mastication.  Appropriately  to  this  motion  the  condyle 
of  the  mandible  is  either  subglobular,  or  is  extended 
anteroposteriorly,  and  the  glenoid  cavity  is  a  longitudi- 
nal instead  of  a  transverse  groove. 

The  mechanical  action  of  the  development  of  the 
rodent  dentition  has  been  as  follows.  The  first  factor 
in  the  order  of  time  and  importance  was  the  increasing 
length  of  the  incisor  teeth.  Those  of  the  lower  jaw 
closed  behind  those  of  the  upper  in  the  progenitors  of 
the  Glires  (e.  g.  Psittacotherium)  as  in  other  Mamma- 
lia. Increase  of  length  of  these  teeth  in  both  jaws  would 
tend  to  keep  the  mouth  permanently  open,  were  it  not 
for  the  possibility  of  slipping  the  lower  jaw  backwards 
as  it  closed  on  the  upper.  This  backward  pressure 
had  undoubtedly  existed,  and  has  operated  from  the 
earliest  beginning  of  the  growth  of  the  rodent  incisors. 
The  process  has  been  precisely  the  opposite  of  that 
which  has  occurred  to  the  Carnivora,  where  the  pres- 
sure has  been  ever  forwards  owing  to  the  development 
of  the  canines.  The  progressive  lengthening  of  the 
incisors  through  use  has  been  dwelt  on  by  Professor 
Ryder  (/.  <:.).  The  posterior  pressure  on  the  lower 
jaw,  produced  by  its  closing  on  the  upper,  has  been 


KINE  TO  GENE  SIS. 


347 


increased  directly  as  the  increase  in  the  length  of  the 
incisors,  especially  those  of  the  lower  jaw. 

The  first  effect  of  this  posterior  pressure  will  have 
been  to  slide  the  condyle  of  the  mandible  posteriorly 


over  the  postglenoid  surface,  if  any  were  present,  as  is 
probable,  in  the  bunotherian  ancestor  of  the  rodent. 
Continued  repetition  of  the  movement  would  probably 
push  the  process  backwards  so  as  to  render  it  ineffec- 
tive as  a  line  of  resistance,  and  ultimately  to  flatten  it 


348    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

out  against  the  otic  bulla,  and  atrophy  it.  The  lower 
jaw  would  thus  come  to  occupy  that  peculiarly  pos- 
terior position  which  it  does  in  all  rodents. 

The  anteroposterior  (proal1)  type  of  mastication 
becoming  necessary,  an  appropriate  development  of 
the  muscles  moving  the  lower  jaw,  with  their  inser- 
tions, follows,  pari passu.  As  a  result  we  see  that  the 
insertion  of  the  temporal  muscle  creeps  forward  on  the 
ramus,  until  in  the  highest  rodents  (Cavia)  it  extends 
along  the  ramus  to  opposite  the  first  true  molars.  The 
office  of  this  muscle  is  to  draw  the  ramus  backwards 
and  upwards,  a  movement  which  is  commenced  so 
soon  as  the  inferior  incisor  strikes  the  apex  of  the  su- 
perior incisor  on  the  posterior  side.  By  this  muscle 
the  inferior  molars  are  drawn  posteriorly  and  in  close 
apposition  to  the  superior  molars.  Connected  with 
this  movement,  probably  as  an  effect,  we  find  the  co- 
ronoid  process  of  the  mandible  to  have  become  grad- 
ually reduced  in  size  to  complete  disappearance  in 
some  of  the  genera,  e.  g.  of  Leporidae.  In  these  gen- 
era the  groove-like  insertion  of  the  temporal  muscle 
develops  as  the  coronoid  process  disappears. 

As  third  and  fourth  effects  of  the  posterior  position 
of  the  lower  jaw,  we  have  the  development  of  the  in- 
ternal pterygoid  and  masseter  muscles  and  their  inser- 
tions and  origins.  The  angle  of  the  ramus  being  forced 
backwards,  these  muscles  are  gradually  stretched  back- 
wards at  their  insertions,  and  their  contraction  be- 
comes more  anteroposterior  in  direction  than  before. 
The  internal  pterygoid  becomes  especially  developed, 
and  its  point  of  origin,  the  pterygoid  fossa,  becomes 
much  enlarged.  The  border  of  the  angle  of  the  man- 
dible becomes  more  or  less  inflected.  In  their  effect 

IPage  318. 


KINETOGENESIS.  349 

on  the  movements  of  the  ramus  they  oppose  that  of 
the  temporal  muscle,  since  they  draw  the  ramus  for- 
wards. They  are  the  effective  muscles  in  the  use  of 
the  incisor  teeth ;  that  is,  in  the  opposition  of  the  in- 
ferior incisors  against  the  superior  from  below  and 
posteriorly.  Hence  the  great  development  of  the  in- 
ternal pterygoid,  and,  in  a  less  degree,  of  the  masse- 
ter.  Both  muscles  tend  also  to  close  the  jaws,  but  at 
a  different  point  in  the  act  of  mastication  from  that  at 
which  the  temporal  acts.  If  we  suppose  the  mouth 
to  be  open,  the  action  of  the  masseter  and  internal 
pterygoid  muscles  draws  the  mandible  forwards  and 
upwards  until  the  incisors  have  performed  their  office, 
or  the  molars  are  in  contact  with  each  other  or  with  the 
food.  They  then  relax,  and  their  temporal  muscle 
continues  the  upward  pressure,  but  draws  the  ramus 
backwards  to  the  limit  set  by  the  adjacent  parts,  caus- 
ing the  act  of  mastication. 

A  fifth  effect  of  the  development  of  the  incisors  and 
of  the  proal  mastication,  is  seen  in  the  position  of  the 
molar  teeth.  The  indefinitely  repeated  strain  and 
pressure  applied  to  the  superior  molars  from  forwards 
and  below  has  evidently  caused  a  gradual  extension  of 
the  maxillary  bone  backwards,  so  that  the  last  molars 
occupy  a  position  much  posterior  to  that  which  they 
do  in  other  orders  of  mammals.  This  is  especially  the 
case  in  such  forms  as  Bathyergus,  Arvicola,  and  Cas- 
toroi'des  (Figs.  107-108),  where  the  last  molars  are  be- 
low the  temporal  fossa,  and  posterior  to  the  orbit. 

A  sixth  effect  of  the  causes  mentioned  has  been  re- 
ferred to  by  Ryder.1  This  is  the  oblique  direction  of 
the  axes  of  the  molar  teeth.  These  directions  are  op- 
posite in  the  two  jaws  ;  upwards  and  forwards  for  the 

1  Proceedings  Philadelphia  Academy,  1877,  p.  314. 


350    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

lower,  and  downwards  and  backwards  for  the  upper. 
The  mechanics  of  this  change  of  direction  from  verti- 
cal in  the  primitive  forms  (Sciuridae)  to  oblique  in  the 


Fig.  108  —Castoroides  ohioensis  Foster ;  two-thirds  natural  size;  skull  from 
below,  a,  incisine  foramen;  b,  pterygoid  fossa  ;  c,  internal  pterygoid  plates; 
d,  fossa  in  basioccipital  bone;  e,  external  auditory  meatus  ;/",  mastoid  pro- 
cess; g;  occipital  condyles  ;  h,  tympania  bulla,  after  Hall  and  Wyman. 

genera  with  prismatic  molars,  is  simple  enough.  The 
inferior  crowns  when  closely  appressed  to  the  supe- 
rior, and  drawn  posteriorly  in  the  direction  of  the  long 
axis  of  the  jaw,  press  and  strain  the  teeth  in  the  two 


KINE  TOG  EN E  SIS. 


351 


directions  mentioned.  The  development  of  the  long 
prismatic  crowns  which  has  proceeded  under  these 
circumstances,  has  been  undoubtedly  affected  by  the 
pressure  and  strain,  and  the  direction  we  find  has  been 
the  result. 

The  seventh  effect  is  in  the  detailed  structure  of 
the  teeth  themselves.  Beginning  with  short  crowns 
with  simple  transverse  crests  (Psittacotherium  and  Sci- 
uridae,  Figs.  106,  109), 
we  reach  through  inter-  ^^a^l  t 

mediate  forms,  crowns 
with  vertical  laminae  of 
enamel,  which  some- 
times divide  the  crown 
entirely  across  (Chinchil- 
lidae,  Caviidae,  Castoroi'd- 
idae)  or  appear  only  on 
the  side  of  the  crown, 
through  the  continued 
coalescence  of  the  prisms 
of  which  each  molar 
crown  is  composed  ( Arvi-  .  Fl*  ^•~(W*JTT' **£*  Leidy,  from 

the  White  River  beds  of  Colorado;  orig- 

COla).  In  many  instances  inal;  from  the  Report  U.  S.  Geol.  Surv 
the  crowns  increase  in  J^'-j*.  cramiam  from  below;  rf,  man- 

dible  from  above. 

transverse  at  the  expense 

of  their  longitudinal  diameter  (Castor,  Lepus).  The 
vertically  laminated  structure  is  evidently  due  to  the 
crowding  together  of  transverse  crests  by  the  same 
pressure  which  has  given  the  crowns  their  oblique  di- 
rection. In  many  genera  the  lengthening  of  the  crown 
has  included  the  lengthening  of  the  longitudinal  con- 
nection between  the  transverse  crests,  as  in  Arvicola, 
Castor,  and  Hystricidae  generally.  In  others  this  con- 
nection has  not  been  continued,  so  that  the  crown  is 


352    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

composed  of  prisms  which  are  separate  to  near  the 
base,  as  in  Amblyrhiza  and  Geomyidae.  In  others,  con- 
nection between  the  prisms  has  been  lost  by  caenogeny, 
as  in  Chinchillidae  and  Caviidae  generally.  The  latter 
families  display  also  the  greatest  amount  of  crowding. 

V.     DISUSE  IN  MAMMALIA. 

Modifications  of  structure  of  the  mammalian  skel- 
eton accompany  the  disuse  of  parts,  no  less  distinctly 
than  in  other  divisions  of  animals.  That  these  modi- 
fications are  the  direct  consequences  of  this  disuse 
may  be  reasonably  inferred  as  the  antithesis  to  the 
thesis  of  development  of  structure  through  use,  main- 
tained in  the  preceding  pages.  The  evidence  is  more 
convincing  from  the  fact  that  the  same  structures  are 
observed  to  be  related  to  similar  dynamic  conditions 
in  groups  of  different  taxonomic  position.  I  select 
four  illustrations  from  the  Mammalia,  from  types  in 
which  the  phylogeny  is  known,  so  that  there  is  no 
question  as  to  the  degeneracy  of  the  parts  described. 

a.   Natatory  Limbs. 

The  limbs  have  undergone  great  modifications  of 
form  in  their  gradual  adaptation  to  aquatic  habits. 
The  stages  of  this  process  are  to  be  observed  first  in 
the  sea-otter  (Enhydra),  then  in  the  seals,  then  in  the 
sirenians,  and  last  in  the  Cetacea.  This  succession 
of  groups  is  not  given  here  as  a  phylogeny,  for  paleon- 
tology does  not  warrant  any  such  history,  but  the  phy- 
logeny of  the  limbs  has  been  similar  in  the  order  of 
succession. 

The  use  of  a  limb  as  an  oar  for  propulsion  in  the 
water  requires  that  it  shall  be,  so  far  as  the  blade  is 
concerned,  inflexible.  Such  a  structure  has  existed  in 


KINE  TOGENESIS. 


353 


all  thoroughly  aquatic  Vertebrata.  This  implies  the 
immobility  of  the  articulations,  which  is  due  to  the 
loss  of  their  condylar  surfaces.  This  may  be  traced 
to  disuse  of  such  articulations.  This  disuse  would  be 
at  first  voluntary,  the  limb  being  held  stifHy  while  used 
as  an  oar  in  the  act  of  swimming.  Loss  of  power  of 
extension  and  flexion  is  well 
known  to  result  from  disuse. 
It  is  well  known  that  the  flex- 
ors and  extensors  of  the  manus 
have  become  atrophied  in  the 
Cetacea.  Not  so,  however, 
with  the  flexors  and  extensors 
of  the  humerus,  which  become 
those  of  the  entire  limb.  In 
the  whales  the  first  segment  of 
the  fore  limb  is  enclosed  within 
the  integument  of  the  body, 
so  that  its  motion  being  much 
restricted,  the  insertional 
crests  are  reduced  in  size.  In 
the  eared  seals  (Otariidae)  the 
hind  limbs  are  somewhat  free 
from  the  body  integument,  so 
that  they  can  be  turned  for- 
ward when  on  land.  They  are 
further  enclosed  in  the  true 

seals  (Phocidae)  so  that  their  motion  is  very  slight  and 
they  cannot  be  used  for  progression  on  land,  and  are 
available  only  for  swimming. 

b.  Abortion  of  Phalanges  in  Ungulata. 

In  the  heavy  Ungulata  the  longitudinal  diameter 
of  the  phalanges  is  greatly  reduced  in  relation  to  their 


Fig.  no. — Bal&na  mysticetus 
fore  limb  :  from  Cuvier,  Oss.  Fos 
sites. 


354    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

transverse.     The  successive  increase  in  depression  in 
the  bones  of  the  feet  with  the  advance  of  time  is  to  be 


most  readily  seen  in  the  order  Amblypoda,  where  we 
pass  from  Pantolambda  to  Coryphodon  and  Uintathe- 


KINETOGENESIS.  355 

rium  (Fig.  1 1 1.)  A  similar  successive  reduction  is  to  be 
seen  in  the  lines  of  the  Perrisodactyla,  as  we  pass  from 
the  smaller  and  lighter  to  the  heavier  and  more  bulky 
types.  Such  series  are  those  which  commence  in  the 
LophiodontidaB,  and  terminate  in  the  Menodontidae  on 
the  one  hand,  and  the  rhinoceroses  on  the  other.  The 
elephants  display  the  end  of  a  similar  line,  which  com- 
mences in  the  Condylarthra.  In  all  of  these  bulky 
mammals  the  weight  in  progression  is  borne  on  the 
extremities  of  the  metapodial  bones,  and  the  phalanges 
take  but  little  share  in  it.  They  are  turned  forwards 
and  are  nearly  useless.  Their  great  reduction  in  di- 
mensions in  these  forms  appears  to  me  to  have  fol- 
lowed disuse,  and  this  is  then  the  probable  cause  of  it. 

c.   Atrophy  of  the  Ulna  and  Fibula. 

Successive  atrophy  of  the  ulna  and  fibula  has  been 
already  referred  to  (p.  135).  This  is  coextensive  with 
reduction  of  the  number  of  the  digits  in  the  ungulate 
Mammalia,  and  with  the  development  of  the  digital 
patagium  in  the  bats.  This  is  in  broad  contrast  to  the 
subequal  development  of  the  ulna  and  radius  in  the 
Cetacea,  where  the  fore  limb  functions  as  the  blade  of 
an  oar.  The  cause  of  the  reduction  of  the  two  ele- 
ments in  the  Ungulata  is  the  restriction  of  the  func- 
tions of  the  fore  and  hind  limb  to  the  radius  and  tibia 
respectively.  The  distal  extremities  of  the  ulna  and 
fibula  are  supported  by  the  external  bones  of  the  carpal 
and  tarsal  series  respectively.  The  reduction  of  the 
external  digit  deprives  the  external  bones  in  question 
of  their  share  in  the  support  of  the  general  weight,  and 
consequently  relieves  them  of  the  impact  which  passes 
through  the  longer  median  digits  which  remain.  The 
median  digits,  on  the  other  hand,  support  the  radius 


356    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

and  tibia  through  the  medium  of  the  carpus  and  tar- 
sus, and  it  is  these  elements  therefore  which  function 
in  the  use  of  the  limb.  We  have  here  an  evident 
illustration  of  the  effect  of  disuse  in  effecting  the 
atrophy  of  an  element,  and  of  use  in  increasing  the 
size  and  complexity  of  an  adjacent  element,  of  the 
same  organism.  No  other  explanation  seems  possible, 
for  the  elements  which  are  reduced  and  those  which 
are  enlarged,  are  subjected  in  every  other  respect  to 
the  same  conditions. 

d.   Atrophy  of  Incisor  Teeth. 

This  is  complete  in  both  jaws  of  existing  Edentata; 
the  upper  jaw  of  Dinocerata  and  many  Artiodactyla, 
and  is  partial  in  the  upper  jaw  in  various  Chiroptera 
and  Lemuridae.  We  have  already  seen  (p.  326)  that 
the  superior  incisors  of  certain  Lemuridae  are  without 
utility,  owing  to  the  conversion  of  the  inferior  incisors 
into  a  horizontal  comb.  I  have  ascribed  the  reduction 
of  the  superior  incisors  of  bats  to  disuse  consequent  on 
the  adoption  of  a  frugivorous  diet.1  Further  reason, 
which  is  common  to  the  living  members  of  the  orders 
mentioned,  is  to  be  found  in  the  disuse  which  has  fol- 
lowed the  use  of  the  tongue  as  an  organ  for  the  pre- 
hension of  food.  The  fruit-eating  bats  with  most  re- 
duced incisors  (Glossophaginae)  carry  the  soft  parts  of 
fruits  into  the  mouth  with  the  tongue.  The  Edentata 
use  the  tongue  for  the  collection  of  both  insect  and 
vegetable  food,  projecting  it  far  exterior  to  the  mouth. 
The  Artiodactyla  without  superior  incisors  however, 
combine  the  prehensile  use  of  the  tongue  with  a  use  of 
the  lower  incisors,  which  bite  off  the  grass  thus  seized, 

\Mechan.   Origin,  etc.,  Mammalia,   1889,  p.  224.     See  also  Dr.   H.   Allen, 
Proceeds.  Academy,  Philadelphia,  1891,  p.  451. 


KINETOGENESIS.  357 

while  it  is  pressed  against  the  pad  which  replaces  the 
superior  incisors.  Why  the  superior  incisors  should 
have  disappeared  in  this  group  is  not  yet  clear  to  my 
mind. 

In  this  connection  Dr.  Allen  (/.  <:.)  reminds  us  that 
in  hypertrophy  of  the  tongue  in  man,  the  inferior  in- 
cisors are  thrown  forward  and  are  widely  separated 
from  each  other.  He  considers  it  reasonable  to  infer 
that  in  lower  animals  where  the  tongue  is  used  for  pre- 
hension, the  similar  change  which  takes  place  in  the 
teeth,  from  a  vertical  to  a  horizontal  position,  is  induced 
by  this  cause. 

Vi.     HOMOPLASSY  IN  MAMMALIA. 

The  direct  evidence  in  favor  of  kinetogenesis  above 
adduced  is  greatly  strengthened  by  corroborative  tes- 
timony presented  by  distinct  phyla  of  animals.  Re- 
stricting myself  here  to  Mammalia,  I  will  enumerate  a 
number  of  cases  where  the  same  structures  have  ap- 
peared in  distinct  lines  of  descent  under  similar  me- 
chanical conditions,  a  phenomenon  already  referred  to 
on  page  72  under  the  name  of  Homoplassy. 

Before  reviewing  the  subject,  I  cite  what  is  the 
most  remarkable  example  of  homoplassy  in  the  Mam- 
malia which  has  yet  come  to  the  knowledge  of  paleon- 
tologists. Ameghino  has  discovered  in  the  Cenozoic 
formations  of  Argentina  a  group  of  Ungulata  which  he 
calls  the  Litopterna,  and  which  I  regard  as  a  suborder 
of  the  Taxeopoda,  allied  to  the  Condylarthra  (p.  128). 
Ameghino  placed  the  group  under  the  Perissodactyla, 
but  the  tarsus  and  carpus  are  of  a  totally  different  char- 
acter, and  indicate  an  origin  from  the  Condylarthra 
quite  independently  of  that  division.  The  carpal  and 
tarsal  bones  are  in  linear  series,  or  if  they  overlap,  it  is  in 


358    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


KINETOGENESIS.  359 

a  direction  the  opposite  of  that  which  characterizes  the 
order  Diplarthra  (=Perissodactyla  and  Artiodactyla). 
But  the  Litopterna  present  a  most  remarkable  paral- 
lelism to  the  Perissodactyla  in  the  characters  of  both 
the  feet  and  the  dentition.  No  genus  is  known  as  yet 
which  possesses  more  than  three  toes  before  and  be- 
hind, and  these  are  of  equal  length  in  Macrauchenia 
Owen.  In  this  genus  the  teeth  are  not  primitive  but 
are  much  modified.  The  most  primitive  dentition  is 
seen  in  the  genus  Proterotherium  (Ameghino)  where 
the  superior  molars  are  tritubercular  as  in  many  Con- 
dylarthra.  In  this  genus  (Fig.  112,  A),  there  are  three 
toes,  but  the  lateral  ones  are  reduced,  about  as  in  the 
Equine  genus  Anchitherium  (p.  148).  In  the  next 
genus,  Diadiaphorus  Ameghino,  the  superior  molars 
are  quadritubercular  and  crested,  while  the  lateral  toes 
are  reduced  still  more,  being  quite  rudimental  (Fig. 
112,  B,  C),  as  in  the  equine  genera  Hippotherium  and 
Prothippus  (p.  149;  Fig.  70).  The  superior  molars 
have  not  progressed  so  far  as  in  these  genera,  but  are 
not  very  different  from  those  of  Anchitherium.  In  the 
third  and  last  type  (Thoatherium  Ameghino),  the  lat- 
eral digits  have  disappeared  from  both  fore  and  hind 
feet  (Fig.  112,  C,D),  so  that  the  condition  is  that  of 
the  genus  Equus  (Fig.  81),  but  the  splints  in  the  Thoa- 
therium crepidatum  Ameghino  are  even  more  reduced 
than  in  the  known  species  of  horse.  The  superior 
molars  have  not  assumed  the  pattern  of  the  genus 
Equus,  but  resemble  rather  those  of  Macrauchenia, 
and  could  have  been  easily  derived  from  those  of  Dia- 
diaphorus. 

Here  we  have  a  serial  reduction  of  the  lateral  digits 
and  their  connections  with  the  leg,  and  increase  in  the 
proportions  of  the  middle  digit  and  corresponding  in- 


360   PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

crease  in  the  proximal  connections,  exactly  similar  to 
that  which  took  place  in  the  horse-line,  in  a  different 
order  of  Mammalia. 

In  review  I  now  cite  as  examples  of  homoplassy: 

First,  as  regards  the  development  of  the  tongue- 
and-groove  ankle-joint.  This  has  been  developed  in- 
dependently along  four  distinct  phyla,  viz.,  in  the  lepo- 
rid  Glires,  the  Carnivora,  and  the  even  and  odd  toed 
Diplarthra. 

Second,  the  wrist-joint.  The  faceting  of  the  radial 
surface  has  appeared  independently  in  the  perissodac- 
tyle  and  artiodactyle  lines,  but  is  best  developed  in  the 
latter.  Also  it  appeared  independently  in  the  separate 
suoid  and  booid  lines  in  the  latter  suborder. 

Third,  the  trochlear  crest  of  the  elbow-joint  ap- 
peared independently  in  the  perissodactyle  and  artio- 
dactyle Diplarthra,  and  in  the  leporid  Glires  (the  rab- 
bit family). 

Fourth,  the  round  head  of  the  radius  appeared  in- 
dependently in  the  lines  of  the  Edentata  (ant-eater) 
and  Quadrumana,  under  the  stress  of  supination  of 
the  hand. 

Fifth,  the  development  of  cusps  with  crescentic  sec- 
tion out  of  cusps  with  round  section  has  occurred  in 
the  widely  different  groups  of  the  multituberculate 
Prototheria,  and  the  selenodont  Artiodactyla.  In  the 
former  the  crescents  are  transverse,  since  the  thrust  of 
the  teeth  in  use  is  longitudinal ;  in  the  latter  they  are 
longitudinal,  since  the  thrust  of  the  jaws  is  transverse. 

Sixth,  the  deep  plication  and  hypsodcnty  of  molars 
appeared  independently  in  the  Glires,  Tillodonta,  Pro- 
boscidia,  Sirenia,  Perissodactyla,  and  Artiodactyla  ; 
and  probably  in  the  Edentata  and  Toxodontia. 

Seventh,  increase  in  the  length  of  the  legs  has  en- 


KINETOGENESIS.  361 

sued  in  the  Marsupialia,  Glires  (Lepus,  Dolichotis, 
Dipus),  Carnivora,  Ungulata,  Quadrumana. 

Eighth,  reduction  of  digits  has  occurred  under  sim- 
ilar conditions  in  Marsupialia,  Glires,  Insectivora, 
Carnivora,  Ungulata. 

Ninth,  the  atrophy  of  the  ulna  and  fibula  occur  in 
the  distinct  lines  of  the  Perissodactyla  and  Artiodac- 
tyla,  and  the  atrophy  of  the  fibula  in  the  leporid 
Glires  ;  all  in  limbs  which  function  in  the  most  rapid 
progression. 

Further  confirmation  of  the  law  of  kinetogenesis  is 
to  be  found  in  those  cases  where  different  structures 
appear  in  different  parts  of  the  skeleton  of  the  same 
individual  animal,  in  direct  correspondence  with  the 
different  mechanical  conditions  to  which  these  parts 
have  been  subjected.  Examples  :  the  diverse  modifi- 
cations of  the  articulations  of  the  limbs  in  consequence 
of  the  uses  to  which  they  have  been  put,  in  mammals 
which  excavate  the  earth  with  one  pair  of  limbs  only; 
as  in  the  anterior  limbs  of  the  fossorial  Edentata,  In- 
sectivora, and  Glires.  The  reduction  of  the  number 
of  the  digits  in  the  posterior  limb  only  when  this  is 
extensively  used  for  rapid  progression,  as  in  leaping : 
this  is  seen  in  the  kangaroo  and  jerboas,  in  the  orders 
Marsupialia  and  Glires. 

The  development  of  a  dental  structure  of  premolars 
identical  with  that  of  the  molars,  from  a  different  struc- 
tural origin,  in  the  Perissodactyla. 

From  the  preceding  facts  I  have  inferred  that  in 
biologic  evolution,  as  in  ordinary  mechanics,  identical 
causes  produce  identical  results. 


362    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


VILA    HYPOTHESIS    OF    THE    ORIGIN    OF    THE    DIVISIONS  OF 
THE  VERTEBRATA. 

In  order  to  estimate  the  part  which  has  been 
played  by  the  movements  of  the  Vertebrata  in  chang- 
ing their  environment  in  past  geologic  ages,  we  have  to 
rely  principally  on  inferences  derived  from  the  present 
physical  characteristics  of  the  earth.  Formerly,  as 
now,  conditions  of  temperature,  humidity,  soil,  shel- 
ter, food,  etc.,  were  avoided  or  appropriated  by  ani- 
mals, through  their  capacity  for  moving  from  place  to 
place.  What  concerns  us  chiefly  here,  is  the  effects 
on  their  structure  produced  by  the  movements  of  Ver- 
tebrata. In  examining  this  question  I  will  take  it  up 
in  systematic  order,  so  as  to  observe  whether  kineto- 
genesis  has  been  the  principal  or  only  a  subordinate 
agency  in  the  evolution  of  this  branch  of  the  animal 
kingdom. 

The  most  conspicuous  index  of  the  serial  succes- 
sion of  the  vertebrate  classes,  is,  as  has  been  already 
remarked,  the  circulatory  system.  The  modifications 
of  this  system  have  been  immediately  connected  with 
those  of  the  method  of  respiration,  which  the  exigen- 
cies of  the  environment  induced  in  vertebrates.  The 
existence  of  branchial  arteries  and  veins  dates  from 
the  earliest  vertebrate,  if  not  from  prevertebrate  life. 
They  are  already  established  in  the  Tunicata,  and  con- 
tinued throughout  the  rising  scale  in  diminished  num- 
bers, so  long  as  Vertebrata  were  exclusively  aquatic 
in  their  modes  of  life.  When  at  the  close  of  the  De- 
vonian system  the  land  masses  assumed  great  propor- 
tions in  both  the  Eastern  and  Western  Hemispheres, 
it  is  probable  that  many  fishes  were  entangled  in  shal- 


KINE  TO  GENESIS.  363 

low  water,  which  rapidly  freshened,  and  ultimately 
were  desiccated,  and  respiration  by  the  swallowing  of 
air  into  the  alimentary  canal  began  to  take  the  place 
of  respiration  by  gills.  It  is  well  known  that  respira- 
tion by  this  means  may  be  carried  on  by  fishes  of  va- 
rious genera,  e.  g.  Cobitis  ;  and  Professor  Gage  has 
shown  that  the  same  habit  exists  in  Batrachia  and  in 
certain  tortoises  (Tronychidae).  In  the  middle  Car- 
boniferous shales  tracks  of  land  animals  occur,  and 
the  bones  of  Batrachia  abound  in  the  coal  measures. 
Already  in  the  Permian  these  Batrachia  are  accompa- 
nied by  numerous  Reptilia,  and  air  breathers  of  ter- 
restrial habits  had  become  numerous  on  the  earth. 

The  habit  of  holding  in  the  oesophagus  large  quan- 
tities of  air  while  engaged  in  seeking  food  in  foul 
water,  or  on  land,  on  the  part  of  vertebrates  which 
normally  oxygenated  the  blood  by  means  of  gills,  was 
probably  the  mechanical  cause  of  the  development  of 
a  pouch,  and  afterwards  of  a  diverticulum  of  the 
oesophagus,  which  became  ultimately  a  swim-bladder 
or  a  lung.  In  vertebrates  in  which  a  return  to  aquatic 
life  became  necessary,  it  became  the  former;  in  those 
which  remained  for  a  shorter  or  longer  period  of  time 
on  land  it  became  the  latter.1  It  is  noteworthy  that 
among  fresh-water  fishes  generally,  the  swim-bladder 
is  more  complex  than  among  marine  forms,  showing 
that  the  varying  conditions  of  shore  and  fresh-water 
life  have  been  mainly  responsible  for  its  development. 

The  development  of  a  lung  at  once  produced  a 
change  in  the  uses  to  which  the  various  branchial 
arches  were  put.  The  posterior,  which  supply  the 
lung,  would  be  subjected  to  greater  pressure  owing  to 
the  increased  blood  supply  demanded  by  the  lung, 

IThis  view  is  adopted  by  C.  Morris,  American  Naturalist,  1892,  p.  975. 


364    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

and  a  correspondingly  diminished  pressure  would  be 
experienced  by  the  now  unused  branchial  portions  of 
the  bows.  The  first  would  retain  the  importance  of  its 
basal  portion,  as  the  source  of  the  carotids,  while  the 
middle  arches  would  continue  their  existence  as  the 
bases  of  the  central  dorsal  aorta.  The  loss  of  the  right 
aorta-root  in  Mammalia  was  probably  due  to  the  fact 
that  the  great  arteries  which  supply  the  digestive  sys- 
tem are  primitively  branches  of  the  left  aorta-root,  as 
they  are  to-day  in  the  crocodiles  and  in  many  of  the 
Batrachia.  The  right  aorta-root  disappeared  through 
disuse.  Probably  in  the  immediate  ancestors  of  the 
birds,  as  in  the  crocodiles,  the  right  aorta-root  gave 
off  the  carotides  and  the  subclaviae.  As  the  birds  de- 
mand an  excessive  blood-supply  for  the  fore  limbs,  we 
have  here  probably  the  reason  why  the  right  root  re- 
mained in  this  subclass. 

The  next  index  of  successional  development  in  Ver- 
tebrata  is  the  brain.  Our  belief  that  use  under  stimu- 
lus has  been  the  cause  of  its  successive  growth,  can 
only  be  based  on  the  analogy  of  our  own  experiences 
in  the  matter  of  education.  No  part  of  the  human 
organism  is  so  susceptible  to  stimuli  as  the  nervous 
system,  and  the  marvellous  effects  on  faculty  of  con- 
tinued exercise  are  well  known  to  everybody.  Since 
the  changes  of  mental  states  are  necessarily  due  to 
corresponding  structural  changes  no  one  will  find  in 
ignorance  of  the  mechanics  of  brain-evolution  a  serious 
obstacle  to  believing  that  it  has  taken  place  under  the 
influence  of  the  innumerable  stimuli  always  present  to 
animal  life. 

It  is  in  the  skeleton  that  we  have  the  actual  record 
and  evidence  of  the  effect  of  movement  on  structure. 
It  must  be  remembered  in  this  connection  that  skeletal 


KINETOGENESIS.  365 

and  dental  tissues  exhibit  the  phenomena  of  nutrition 
and  waste  (metabolism),  common  to  all  living  organic 
matter.  Hence  even  the  hardest  osseous  tissues  are 
plastic  and  are  subject  to  mechanical  influences  to  a 
degree  which  is  not  possible  to  dead  matter  of  equal 
density. 

Fundamental  differences  between  Vertebrata  are 
displayed  by  their  organs  of  movement,  but  before 
specially  considering  these  I  will  refer  briefly  to  cer- 
tain other  fundamental  characters  displayed  by  the 
skull.  In  advancing  from  the  fishes  to  the  Mammalia 
we  observe  a  successive  consolidation  of  the  mandibu- 
lar  arch,  and  of  its  mode  of  connection  with  the  cra- 
nium. The  mandibular  arch  in  its  entirety  displays  in 
the  fishes  a  segmented  condition,  generally  compar- 
able to  that  which  characterizes  the  branchial  arches. 
Among  Batrachians  and  Reptilia  various  degrees  oi 
fixation  of  its  suspensor  (hyomandibular,  quadrate)  to 
the  cranium  exist,  and  in  some  of  them  it  is  closely 
united  by  immovable  suture.  The  complete  fusion 
with  the  squamosal  seen  in  the  Mammalia  is  its  final 
status.  The  segmentation  of  the  mandibular  portion 
of  the  arch  seems,  from  the  discoveries  of  Ameghino, 
to  have  continued  among  some  of  the  Lower  Eocene 
mammals,  but  that  finally  disappeared,  so  that  in  the 
modern  mammals  the  movable  mandibular  arch  con- 
sists of  a  single  element  on  each  side.  In  this  history 
we  see  an  instance  of  the  progressive  coossification  of 
parts,  which  results  from  the  constant  strain  of  use,  of 
which  many  other  normal  and  abnormal  examples  are 
known.  This  use  is  the  act  of  mastication.  Where 
there  is  no  mastication,  and  the  jaws  are  used  only  as 
prehensile  organs,  this  coossification  does  not  occur, 
as,  for  instance,  in  the  snakes.  In  this  most  special- 


366   PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

ized  and  modern  type  of  Reptilia,  the  segmentation  te 
complete. 

The  segmentation  of  the  limbs  in  the  Vertebrata  is 
a  simple  mechanical  problem.  Paleontology  and  em- 
bryology concur  in  proving  that  the  limbs  originated 
in  primitive  folds  in  the  external  integument,  and  that 
their  connection  with  the  internal  skeleton  was  of  later 
accomplishment,  has  been  shown  by  Wiedersheim. 
At  first  free,  they  sought  points  of  support  on  the 
skeleton,  but  did  not  lose  their  free  mobility  when 
this  contact  was  attained.  Appropriately  to  the  me- 
chanical conditions  of  rigidity  and  flexibility  neces- 
sary to  their  use  in  a  fluid  medium,  they  were  orig- 
inally composed  of  slender  rods  which  were  segmented 
by  interruptions  at  suitable  points.  The  articulations 
of  the  fin-rays  of  fishes  have  been  made  the  subject 
of  an  interesting  research  by  Ryder,  who  finds  them 
to  be  fractures,  due  to  flexures  during  motion  in  the 
water  medium.1  The  limb  of  land  vertebrates  (the 
chiropterygium)  was  derived  from  one  of  the  forms  of 
fins  (rhipidopterygium)  of  water  vertebrates.  This  is 
the  simple  type  of  primitive  fin  displayed  by  the  Pale- 
ozoic Teleostomi  of  the  superorder  Rhipidopterygia. 
Whether  the  subdivisions  of  the  chiropterygium,  the 
propodial,  metapodial,  and  phalangeal  bones,  etc., 
were  divided  from  the  primitive  branches  of  the  archi- 
pterygium,  as  held  by  Gegenbaur,  or  whether  they 
have  developed  by  sprouting  from  a  simple  axial  series 
of  segments,  as  held  by  Baur,  or  whether,  as  I  have 
suggested,  it  is  a  derivation  from  the  rhipidopterygian 
type  of  paired  fin,  is  not  yet  decided.  In  either  case, 
the  limbs  of  the  first  land  animals  were  segmented  and 
flexible  at  the  joints  between  the  segments.  The  ne- 

\Proceedings  of  the  American  Philosophical  Society,  1889,  p.  547. 


KINE  TO  GENESIS.  367 

cessities  of  such  limbs  are  twofold :  first,  to  serve  as 
supports  when  at  rest  or  in  progression  ;  second,  to  be 
applied  to  the  body  in  protection  from  enemies,  or  in 
aiding  the  functions  of  feeding,  reproduction,  etc. 
The  first  function  requires  principally  mobility  at  the 
point  of  connection  with  the  body.  The  second,  flexi- 
bility at  some  point  on  the  shaft  of  the  limb.  The  two 
kinds  of  movements  in  question  would  conserve  two 
principal  points  of  flexure,  and  these  would  be  for  the 
fore  limb,  just  what  we  find,  the  shoulder  and  elbow 
joints;  and  for  the  hind  limbs,  the  hip  and  knee  joints. 
The  two  median  joints  are  directed  in  opposite  ways, 
the  elbow  backwards  and  the  knee  forwards.  This 
diversity  is  clearly  due  to  the  diverse  positions  of  the 
functioning  regions.  The  opposite  extremities  of  the 
alimentary  canal,  the  posterior  including  the  exits  of 
the  urogenital  organs,  requires  that  the  fore  limbs 
should  bend  forwards,  and  the  posterior  limbs  back- 
wards. And  the  constantly  recurring  necessity  for  the 
exercise  of  these  flexures  must  necessarily  have  devel- 
oped the  appropriate  articulations  in  preference  to  all 
others.  The  terminal  flexure,  that  of  the  wrist  or 
ankle,  has  been  evidently  due  to  a  similar  mechanical 
cause,  viz.,  the  flexure  due  to  pressure  of  the  weight 
of  the  body  on  the  terminal  segments  when  in  contact 
with  earth.  The  distal  segments  are  the  most  slender 
in  all  types,  and  least  able  to  maintain  a  linear  direc- 
tion under  pressure,  hence,  they  have  flexed  easily  and 
thus  the  line  of  separation  between  leg  and  foot  had 
its  origin.  The  ankle  and  wrist  in  the  Batrachia  Uro- 
dela  is  still  a  mere  flexure. 

Mr.  Herbert  Spencer  has  endeavored  to  account  for 
the  origin  of  the  segmentation  of  muscles  into  myo- 
tomes,  and  the  division  of  the  sheath  of  the  notochord 


368    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

into  vertebrae,  by  supposing  it  to  be  due  to  the  lateral 
swimming  movements  of  the  fishes,  which  first  exhibit 
these  structures.1  With  this  view  various  later  authors 
have  agreed,  and  I  have  offered  some  additional  evi- 
dence of  the  soundness  of  this  position  with  respect  to 
the  vertebral  axis  of  Batrachia,2  and  the  origin  of  limb 
articulations.3  It  is  true  that  the  origin  of  segmenta- 
tion in  the  vertebral  column  of  the  true  fishes  and  the 
Batrachia  turns  out  to  have  been  less  simple  in  its  pro- 
cess than  was  suggested  by  Mr.  Spencer,  but  his  gen- 
eral principle  holds  good,  now  that  paleontology  has 
cleared  up  the  subject. 

The  Echinodermata,  Mollusca,  Arthropoda,  and 
Vertebrata  possess  external  or  internal  calcareous  or 
chitinous  skeletons  for  the  most  part.  The  lower  forms 
of  all  these  branches,  however,  are  more  or  less  deficient 
in  this  kind  of  protection,  and  embryology  indicates 
that  all  of  them  are  the  descendants  of  the  Vermes  or 
worms,  which  are  mostly  without  such  hard  supports 
and  protections.  Whether  this  be  demonstrated  or 
not,  we  have  plenty  of  evidence  to  show  that  the  prim- 
itive Vertebrata  were  without  hard  skeletons,  and  that 
their  bodies  were  composed  internally  and  externally 
of  perfectly  flexible  tissues. 

If  we  now  imagine  that  either  the  integuments,  or 
an  axial  rod,  of  a  worm-like  animal  has  become  the  seat 
of  a  calcareous  or  chitinous  deposit,  it  is  evident  that 
the  movements  of  the  animal  in  swimming  or  creeping 
must  have  interrupted  the  deposit  at  definite  points  of 
its  length.  The  lateral  flexure  of  the  body  would  be 
restricted  to  certain  points,  and  the  intervening  spaces 

1  Principles  of  Biology ,  1873,  pp.  198-204. 

2  Origin  of  the  Fittest,  1887,  p.  305. 

3  Mechanical  Causes  of  Origin  of  Hard  Parts  of  Mammalia,  1889,  p.  163. 


KINETOGENESIS.  369 

would  become  the  seat  of  the  deposit.  At  the  lines  of 
interruption  joints  would  be  formed,  and  if  the  move- 
ments were  habitually  symmetrical,  these  interruptions 
would  be  equidistant.  In  this  way  the  well-known 
segmentation  of  the  external  skeletons  of  Arthropoda, 
and  the  internal  skeletons  of  Vertebrata  would  be 
formed.  We  have  more  detailed  evidence  that  this 
has  been  the  case.  Thus  the  segmentation  of  the  os- 
seous sheath  of  the  chorda  dorsalis  in  both  primitive 
fishes  and  batrachians  has  been  accomplished  in  wedge- 
shaped  tracts  precisely  as  may  be  observed  in  the  fold- 
ing of  a  tolerably  stiff  sleeve  of  a  coat  which  ensheathes 
the  arm,  under  the  influence  of  lateral  flexures.  The 
wedge-shaped  tracts  are  superior  and  inferior,  the 
apices  directed  towards  each  other.  Seen  from  the 
side  they  form  two  wedges  with  their  apices  together, 
and  their  bases  one  up  and  the  other  down.  Now,  if 
a  person  who  wears  a  coat  of  rather  thick  material  will 
examine  the  folds  of  his  sleeve  as  they  are  produced 
on  the  inner  side  of  his  arm,  he  will  see  a  figure  nearly 
like  that  of  the  segments  of  the  vertebral  column  de- 
scribed. The  folds  will  correspond  to  the  sutures,  and 
the  interspaces  to  the  bony  segments.  He  will  find 
that  the  spaces  are  lens-shaped,  or,  when  viewed  in 
profile,  wedge-shaped,  with  the  apices  together.  This 
arrangement  results  from  the  necessary  mechanics  of 
flexure  to  one  side.  In  flexure  of  a  cylinder  like  the 
sleeve,  or  like  a  vertebral  column,  the  shortest  curve 
is  along  the  line  of  the  greatest  convexity  of  the  cylin- 
der. Here  is  the  closest  folding  of  the  sheath,  and 
here,  consequently,  the  lines  of  fold  in  soft  material, 
or  interruption  in  hard  material,  will  converge  and 
come  together.  That  is  just  what  they  do  in  both  the 


370   PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

sleeve  and  the  rhachitomous  vertebral  column,  the 
only  difference  being  that  in  the  animal  it  is  exhib- 
ited on  both  sides, 


on  onlv  one 

This  difference  is, 
of  course,  due  to 
the  fact  that  the 
animal  can  bend 
himself  in  both  di- 
rections, while  the 
arm  only  bends  in 
one  direction. 

It  results  from 
the  above  obser- 
vations that  the 
structure  of  the 
rhachitomous  ver- 
tebral column  has 
been  produced  by 
the  movements  of 

the  body  jrom  side 

to  side,  as  in  swim- 
ming, during  the 
process  of  the  de- 
posit of  mineral  ma- 
terials and  around 
the  chorda  dorsa- 
lis.1 

^Njpfcf  See  figures  113 

™—-  to  1140  where    the 

coat-sleeve  is  com- 
pared with  the  "rhachitomous"  vertebrae  of  primitive 

1  See  American  Naturalist,  January,  1884. 


372    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

fishes  (Merospondyli  *)  and  Batrachia  (Rhachitomi). 
Such  was  the  origin  of  the  segmentation  in  the  primi- 
tive sharks,  Pleuracanthus,  whose  structure  has  been 
pointed  out  by  Sauvage,  and  Hybodus,  whose  charac- 
ters have  been  demonstrated  by  Smith  Woodward. 
The  segmented  (or  rhachitomous,  as  I  have  termed  it,) 
condition  may  be  then  regarded  as  the  primitive  one  of 
the  osseous  column  in  the  Vertebrata.  From  the  rha- 
chitomous column  two  divergent  lines  have  arisen  as 
already  remarked  (pp.  89,209).  The  inferior  segment 
has  been  retained  in  the  fish-batrachian  line,  whence  I 
have  termed  their  vertebrae  ' '  intercentral,"  while  these 
bodies  have  disappeared  or  become  rudimental  in  the 
higher  Vertebrata.  The  pleurocentra  (Figs.  113-1140, 
<:,  //. )  have,  on  the  other  hand,  developed  downwards, 
and,  meeting  below,  have  formed  the  effective  centrum 
of  the  vertebra.  Hence,  in  the  Monocondylia  and 
Mammalia  the  vertebras  are  "central." 

The  Reptilia  display  a  greater  variety  of  vertebral 
articulation  than  any  of  the  classes  of  Vertebrata. 
After  the  primitive  biconcave  (amphiccelous)  type  was 
abandoned,  the  two  principal  types  assumed  are  the 
ball  and  socket  (proccelous  and  opisthoccelous),  and 
the  plane  (amphiplatyan).  In  those  families  in  which 
the  body  is  more  or  less  in  contact  with  the  ground, 
owing  to  the  absence,  shortness,  or  position  of  the 
limbs  (Lacertilia,  Ophidia),  the  vertebral  bodies  ex- 
hibit the  ball-and-socket  articulation,  while  in  types 
with  longer  limbs  which  supported  the  body  in  pro- 
gression, so  that  the  latter  never  reached  the  ground 
(Dinosauria),  the  articulations  are  plane.  The  ball-and- 
socket  articulation  may  be  inferred  to  have  been  pro- 

1  Zittel,  Handbuch  der  Pal&ontologie ,  III.,  p.  138,  1887,  where  this  charac- 
ter is  first  clearly  pointed  out  in  fishes. 


KINE  TO  GENESIS.  373 

duced  by  vermiform  movements  which  utilize  points  of 
resistance  on  the  earth  as  aids  to  progression,  while  the 
plane  articulation  has  probably  resulted  from  the  per- 
sistence of  the  fixed  relation  which  is  appropriate  to  a 
body  which  should  be  relieved  by  the  legs  of  all  share 
in  movements  necessary  to  progression.  That  this 
position  is  correct  is  sustained  by  the  fact  that  the  cer- 
vical vertebrae  of  various  reptiles  and  mammals  which 
have  plane  dorsal  vertebrae  have  the  ball-and-socket 
structure.  This  is  probably  due  to  the  constant  flex- 
ures to  which  that  part  of  the  column  has  been  sub- 
jected, as  compared  with  the  fixity  of  the  dorsal  re- 
gion. 

Owing  to  the  comparatively  advanced  state  of  our 
knowledge  of  the  phylogeny  of  the  Mammalia  (Chap- 
ter II.),  this  class  furnishes  especial  opportunities  for 
the  study  of  kinetogenetic  evolution.  But  our  knowl- 
edge is  not  yet  sufficiently  complete  to  enable  us  to 
account  on  mechanical  grounds  for  the  origin  of  all 
the  characters  which  distinguish  all  its  subdivisions. 
This  being  the  case,  I  have  not  presented  the  subject 
in  taxonomic  order,  but  have  contented  myself  with 
offering  it  in  the  order  of  evidential  value.  I  have  first 
described  certain  cases  where  the  action  of  kinetogen- 
esis  is  self-evident.  This  has  been  followed  by  the 
presentation  of  cases  where  the  evidence  amounts  to  a 
high  degree  of  probability. 

Referring  now  to  the  table  of  definitions  of  the  or- 
ders of  Mammalia  on  pages  127-128,  I  will  go  over  the 
characters  seriatim,  and  show  how  far  our  knowledge 
warrants  us  in  giving  a  kinetogenetic  explanation  of 
their  origin.  No  mechanical  cause  can  be  at  present 
assigned  for  the  loss  of  the  coracoid  and  episternal 
bones  in  the  Eutheria.  In  the  Eutheria  the  presence 


374    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

of  the  marsupial  bones  of  the  Didelphia  is  a  survival, 
and  it  may  be  that  their  absence  in  the  Monodelphia 
is  due  to  disuse,  on  the  withdrawal  of  strain  on  the 
abdominal  walls  which  followed  the  abandonment  of 
the  oviparous  habit  of  the  Prototheria,  and  the  young- 
bearing  habit  of  the  Marsupialia.  The  very  consider- 
able weight  actually  borne  by  existing  forms  and  prob- 
able weight  carried  by  extinct  forms  will  probably 
account  for  the  development  of  these  bones  through 
strain  on  the  prepubic  cartilage.  The  perforate  palate 
is  a  reptilian  survival,  and  the  closure  of  the  fonta- 
nelles  may  have  been  due  to  the  increased  strain  due 
to  the  increased  energy  of  mastication  which  early  en- 
sued, owing  to  the  increased  size  and  specialization  of 
the  molar  teeth.  Of  the  three  divisions  of  the  Mono- 
delphia, the  Mutilata,  Unguiculata,  and  Ungulata, 
the  Unguiculata  possess  modifications  of  a  character 
of  ungual  phalanges  inherited  from  the  Reptilia,  while 
the  other  two  groups  have  experienced  still  greater 
modification.  The  limbs  of  the  Mutilata  display  the 
result  of  disuse  as  to  the  posterior  ones,  and  special 
use  as  to  the  anterior,  as  I  have  already  pointed  out. 
The  Sirenia  display  a  less  degree  of  modification  than 
the  Cetacea.  The  hoofs  of  the  Ungulata  may  well 
have  assumed  their  laterally  expanded  and  transverse 
forms  by  the  extreme  pressure  and  impact  on  the 
earth,  incident  to  their  function  as  supports. 

The  origins  of  most  of  the  dental  characters  which 
characterize  the  orders  of  Mammalia  have  already  been 
referred  to  mechanical  causes,  and  have  been  already 
treated  of.  The  same  is  true  of  tarsal  and  carpal 
characters,  which  are  of  so  much  importance  among 
the  Ungulata. 

The  characters  enumerated  on  page  139  as  indicat- 


KINETOGENESIS.  375 

ing  progressive  modification  in  time  have  also  been 
mainly  accounted  for  on  mechanical  grounds. 


5.  OBJECTIONS  TO  THE  DOCTRINE  OF  KINETOGENESIS 

It  has  been  objected  that  Neo-Lamarckians  are 
self-contradictory  and  illogical  in  their  defense  of  the 
doctrine  of  the  development  of  structures  by  use,  or 
by  motion.  It  is  asserted  that  they  believe  that  stimuli 
of  different  kinds  produce  similar  results,  and  that 
stimuli  of  the  same  kind  may  produce  different  re- 
sults. The  charge  that  Neo-Lamarckians  hold  those 
views  is  correct,  but  it  is  not  correct  to  suppose  that 
they  are  illogical  or  self-contradictory.  This  criticism 
is  one  of  those  generalities  which  will  not  bear  exam- 
ination, while  the  doctrine  of  kinetogenesis  will  bear 
examination. 

Thus  it  has  been  experimentally  shown  that  bone 
irritation  will  produce  both  bone  deposit  and  bone  ab- 
sorption, according  to  the  degree  of  irritation.  Mode- 
rate irritation  produces  deposit,  and  greater  irritation 
produces  absorption.  Hence  it  is  that  both  impact 
and  strain,  or  pressure  and  stretching,  will  elongate  a 
bone,  by  stimulating  growth,  if  not  excessive.  We 
have  the  illustrations  in  the  elongation  of  ligaments 
and  cartilages  and  their  ossification  under  stretching, 
and  the  shortening  of  both  in  absence  of  use,  from 
which  we  may  infer  their  lengthening  under  use.  The 
continued  lengthening  of  the  limbs  and  teeth  of  the 
higher  Mammalia,  in  the  course  of  geologic  time,  is 
an  illustration  of  the  effect  of  continued  impact  and 
transverse  strain  ;  while  the  lengthening  of  the  limb 
bones  of  the  sloth,  and  of  the  tarsal  bones  of  many 
bats,  is  a  consequence  of  longitudinal  strain. 


376    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

The  differing  directions  of  the  elements  entering 
into  the  articulations  of  the  limbs  of  Mammalia  may 
be  cited  in  illustration  of  the  supposed  inconsistency 
of  supposing  them  all  to  be  the  result  of  impact  and 
strain.  Thus  most  of  the  condyles  are  directed  distad, 
but  the  heads  of  the  humerus  and  femur,  and  the  prox- 
imal surfaces  of  the  carpus  and  tarsus  are  directed 
proximad  (except  the  trochlear  groove  of  the  astraga- 
lus when  present).  So  far  as  regards  the  distal  ends 
of  the  radius  and  tibia  (fore  arm  and  leg)  I  have 
pointed  out  that  here  dense  layers  disposed  longitudi- 
nally impinge  on  a  similar  layer  disposed  transversely, 
with  the  natural  consequence  the  latter  has  yielded  to 
the  excess  of  impact  so  produced.  The  direct  relation 
of  the  sculpture  of  the  surfaces  concerned,  to  the 
lengthening  of  the  foot  and  increase  of  speed  of  the 
animal,  and  hence  increase  of  force  of  impact,  leads 
irresistibly  to  this  conclusion.  As  regards  the  con- 
vexity of  the  heads  of  the  humerus  and  femur,  or  rather 
the  concavity  of  the  corresponding  surfaces  of  the 
scapula  and  acetabulum  the  explanation  has  been  al- 
ready given.  Henke  was  apparently  the  first  to  call 
attention  to  the  fact  that  the  concavity  and  convexity 
of  the  articular  surfaces  is  directly  related  to  the  posi- 
tions of  the  insertions  of  the  muscles  which  move  them. 
He  shows  that  a  concave  surface  is  developed  at  the 
extremity  which  is  nearest  to  the  muscular  insertion, 
while  the  convex  surface  is  developed  on  the  extremity 
which  is  most  remote  from  its  muscular  insertion. 
Thus  is  accounted  for  the  apparently  contradictory 
evidence  of  the  limb  articulations  mentioned.  In  some 
cases  at  least,  as  those  of  the  glenoid  cavities  of  the 
scapula,  ilium,  and  phalanges,  the  muscular  insertions 
are  so  near  to  their  borders,  as  to  suggest  that  the 


K1NE  TO  GENESIS.  377 

growth  of  the  latter  is  due  to  a  pulling  strain  on  them, 
as  well  as  to  the  greater  mobility  of  the  element  which 
becomes  convex,  as  supposed  by  Fick. 

It  is  claimed  in  the  preceding  pages,  that  impacts 
on  the  extremities  of  a  bone  or  tooth,  gradually  in- 
crease its  length.  It  may  be  hastily  supposed  that  in 
this  assumption  I  derive  elongation  of  the  shaft  of  a 
bone  from  the  same  stimulus  which  produces  excava- 
tion and  therefore  abbreviation  of  its  extremities.  In 
the  gross  this  charge  is  correct  j  but  the  position  I 
have  assumed  is  defensible,  because  in  detail  it  is  easy 
to  perceive  that  effect  of  the  use  of  a  limb  on  an  ar- 
ticular surface  of  a  bone  is  quite  distinct  from  that 
which  it  has  on  the  shaft.  At  the  articular  faces  we 
have  discontinuity;  and  therefore  frtctwn ;  in  the  shaft 
we  have  only  the  concussions  produced  by  impact,  to- 
gether with  some  torsion  strain.  That  the  former 
movement  stimulates  the  development  and  activity  of 
the  osteoclasts  has  been  shown  by  Koelliker ;  that  the 
latter  may  stimulate  the  activity  of  osteoblasts  is  ren- 
dered highly  probable  from  the  facts  of  pathological 
anatomy.  These  show  that  a  very  slight  modification 
of  stimulus  is  sufficient  to  change  the  building  cells 
into  the  absorbent  cells  and  back  again.  For  the  same 
reason  belief  in  the  elongation  of  bones  under  stretch- 
ing strain  may  not  be  inconsistent  with  belief  in  an 
elongation  under  impacts. 

Gary  makes  specific  objections  against  the  kineto- 
genesis  of  the  articulations  of  the  mammalian  skele- 
ton.1 After  a  study  of  the  carpus  of  the  Eocene  peris- 
sodactyle  genus  Palaeosyops  he  concludes  that  the 
trapezoid  bone  is  too  small  to  express  properly  the  di- 
rect result  of  purely  mechanical  causes.  He  says  that 

^American  Journal  of  Morphology,  1892,  p.  305. 


378    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION 

in  reaching  this  result  he  has  applied  geometrical  meth- 
ods. "  First,  the  volume  of  the  bones  was  got  at. 
Next  the  area  of  the  bearing  surfaces  and  their  inclina- 
tion to  the  digits  were  measured.  Then  giving  to  the 
thrust  of  each  metacarpal  a  value  proportional  to  its 
volume,  the  distribution  of  that  thrust  can  by  resolu- 
tion and  composition  of  forces,  be  traced  through  the 
foot,  and  the  pressure  on  each  surface  and  bone  ap- 
proximately obtained."  Further  than  this  the  author 
does  not  explain  how  he  reached  the  result  that  the 
trapezoid  is  too  small.  It  is  quite  essential  that  this 
demonstration  should  be  given  if  we  are  expected  to 
accept  his  conclusion.  An  essential  part  of  the  prob- 
lem is,  however,  unnoticed  by  Mr.  Gary ;  and  that  is 
the  condition  of  the  trapezoid  in  the  reptilian  ances- 
tors of  the  Mammalia.  The  phylogeny  of  an  element 
must  be  known,  since  it  furnishes  the  "  physical  basis" 
of  the  problem.  The  fact  is  that  the  trapezium,  trape- 
zoides,  and  the  magnum  owe  their  small  size  to  their 
being  the  only  carpal  elements  which  have  not  been 
produced  by  the  fusion  of  two  or  more  primitive  ele- 
ments of  the  batrachian  and  reptilian  carpus.  The 
trapezoides  moreover  occupies  a  place  in  a  longitudinal 
series  of  three  elements  in  the  primitive  carpus,  while 
the  trapezium  forms  one  of  a  series  of  only  two  ele- 
ments. For  similar  reasons  the  cuneiforms  are  the 
smallest  elements  of  the  tarsus. 

Mr.  Gary  then  proceeds  to  criticize  the  explana- 
tions offered  by  Professor  Osborn  and  myself,  in  ac- 
counting for  the  origin  of  certain  structures.  He  finds 
our  explanations  to  be  self-contradictory,  and  that  we 
also  contradict  each  other.  Osborn  has  supposed  that 
the  conules  of  the  molars  are  produced  by  friction  of 
the  molars  of  opposite  series  on  each  other.  I  have 


KINETOGENESIS.  379 

expressed  the  opinion  that  the  shear  of  the  sectorial 
teeth  of  Carnivora  was  produced  by  lateral  friction 
during  vertical  movement  of  the  lower  tooth  on  the 
upper.  I  have  also  asserted  that  the  forms  of  facets 
of  limb  articulations  are  due  to  pressure.  Mr.  Gary 
sees  here  the  attempt  to  explain  the  origin  of  totally 
different  structures  through  identical  mechanical  pro- 
cesses, and  believes  that  the  attempt  is  a  failure. 
Were  the  conditions  of  the  problems  alike,  as  Mr. 
Gary  thinks  them  to  be,  he  would  have  good  reason 
for  his  opinion.  But  the  conditions  in  the  three  cases 
are  entirely  different,  and  our  author's  conclusion  is 
due  to  neglect  of  the  elementary  facts  of  the  proposi- 
tion. 

The  development  of  conules  at  the  points  indicated 
by  Professor  Osborn,  has  been  supposed  by  him  to 
be  due  to  friction  between  existing  ridges  of  enamel 
which  cross  each  other  when  in  action,  at  the  points 
in  question.  In  the  case  of  the  development  of  the 
sectorial  shear,  the  faces  between  which  the  shearing 
motion  takes  place  are  smooth,  and  without  ridges  or 
crests.  Hence  the  entire  surface  receives  a  homo- 
geneous friction.  In  the  third  case,  that  of  the  foot 
articulations,  there  is  no  friction,  but  there  is  pressure 
which  when  abruptly  applied  in  movement  becomes 
impact.  There  is  really  no  parity  between  the  three 
cases. 

The  author  of  this  paper  also  thinks  that  the  ex- 
planation of  the  elongation  of  bones  through  use  of 
different  kinds  is  not  a  permissible  hypothesis.  He 
cites  my  attempt  to  account  for  the  elongation  of  the 
leg  bones  of  higher  mammals  through  impact-stimulus ; 
and  of  other  limb  bones  of  other  mammals  through 
stretching.  But  he  does  not  prove  that  similar  results 


380    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

may  not  flow  from  mechanical  stresses  applied  in  dif- 
ferent ways.  I  suppose  that  any  mechanical  stress 
which  determines  nutritive  processes  to  a  part,  will  in- 
crease its  size,  cceteris  paribus  ;  and  the  stretch  as  well 
as  the  impact  has  this  effect.  I  have  in  fact  shown,  in 
the  observations  already  cited  (pp.  277-279),  on  the 
production  of  artificial  elbow  joints,  that  osseous  de- 
posit is  stimulated  by  pulling  strain  as  well  as  by  push- 
ing or  impact. 

In  concluding,  Mr.  Gary  admits  one  of  the  two  con- 
tentions of  the  Neo-Lamarckians  in  his  two  closing 
propositions.  He  says  "  Plasticity  of  bone,  using  the 
word  plasticity  not  in  a  physical  sense  merely,  but  to 
include  absorption  under  pressure,  will  probably  ac- 
count for  much  structure  in  the  foot  and  elsewhere, 
especially  the  connection  with  the  joints,  and  in  the 
fields  of  variation  and  correlation."  In  the  second 
proposition  he  says  that  facts  have  been  adduced  by 
him  which  are  inconsistent  with  the  theory  that  the 
size  of  bones  has  been  increased  by  the  stimulus  they 
receive,  and  with  the  theory  that  regions  of  growth  are 
determined  by  regions  of  pressure  and  strain.  "The 
testimony  of  the  literature  as  to  the  latter  point,"  he 
says,  "is  conflicting."  I  have  shown  that  the  supposed 
conflict  is  due  to  a  misunderstanding  on  the  part  of 
the  author  of  this  paper.  The  proposition  that  pres- 
sure does  not  affect  growth  is  in  contradiction  to  the 
admission  made  by  the  author  in  his  first  proposition, 
where  he  admits  that  pressure  determines  structure  ; 
for  in  such  change  of  structure  there  is  always  growth. 
Finally  Mr.  Gary  remarks  "That  race  changes  follow 
those  produced  in  the  individual  life,  or  that  they  are 
directly  caused  by  their  mechanical  surroundings,  I 
do  not  think  it  has  been  satisfactorily  shown."  The 


KINETOGENESIS.  381 

fact  that  the  characters  of  bone  structure  admitted  by 
Mr.  Gary  to  have  had  a  mechanical  origin  appear  in 
the  young  before  birth,  is  evidence  that  race  characters 
are  produced,  in  other  words,  that  they  are  inherited. 

Another  objection  proposed  by  Tomes,  and  quoted 
by  Poulton  and  Wallace  with  approval,  has  reference 
to  the  kinetogenesis  of  teeth  of  Mammalia  as  described 
by  Ryder  and  myself.  Tomes  asserts  that  it  is  quite  im- 
possible that  the  crowns  of  the  teeth  could  have  been 
altered  by  mechanical  impacts  and  strains,  since  their 
form  is  determined  in  the  recesses  of  the  dental  grooves, 
entirely  removed  from  all  the  mechanical  influences 
which  affect  the  external  surfaces  of  the  jaws.  But 
the  observations  of  Koelliker  and  others  show  that 
osteoclasts  are  as  active  in  dental  as  in  ordinary  osse- 
ous tissue.  It  is  altogether  probable  that  the  modifi- 
cations of  dental  structure  have  been  produced  by 
strain  and  friction  under  use  in  the  adult,  precisely  as 
in  the  skeleton,  and  that  the  share  that  the  unerupted 
crowns  have  in  the  process  is  that  of  inheritance  only, 
as  in  the  case  of  .the  skeleton.  That  teeth  deposit  den- 
tine as  process  of  repair  in  adult  mammals  is  well 
known,  and  this  repair  is  in  direct  relation  to  use. 
That  the  effects  of  dental  wear  are  inherited  is  proven 
by  the  fact  cited  by  Tomes  and  Wallace. 

Another  objection  to  the  doctrine  of  kinetogenesis 
which  has  been  made  by  some  of  the  Neo-Darwinians 
is,  that  if  growth  under  stimulus  be  true,  how  can  it 
have  limits,  so  long  as  the  stimulus  of  use  exists.  In 
other  words,  what  is  to  prevent,  in  the  case  of  the 
vertebrate  skeleton,  of  an  indefinite  increase  in  the 
length  of  the  legs,  of  the  teeth,  and  of  their  cusps,  etc. 
The  answer  to  this  objection  will  vary  more  or  less 
with  the  part  of  the  structure  considered.  In  general, 


382     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

however,  it  may  be  assumed  that  stimulus  is  stress 
due  to  a  want  of  harmony  between  an  organism  and 
its  environment,  and  that  kinetogenesis  is  the  result  of 
the  effort  of  the  organism  to  adjust  itself.  So  soon  as 
equilibrium  is  attained,  the  stress  of  stimulus  ceases 
or  is  much  reduced,  and  evolution  in  this  direction 
ceases.  Such  equilibrium  is  attained  when  the  mechan- 
ism of  an  animal  is  sufficient  for  the  satisfaction  of  its 
needs.  When  this  is  the  case  severe  exertion  is  no 
longer  necessary,  and  a  period  of  easy  use  follows 
which  is  sufficient  to  maintain  the  mechanism  in  work- 
ing condition.  In  the  case  where  circumstances  should 
become  so  favorable  for  the  easy  satisfaction  of  the 
necessities  of  life,  as  to  call  for  little  or  no  exertion, 
degeneracy  of  the  organism  is  sure  to  follow.  The 
well-known  phenomena  of  degeneracy  from  disuse 
show  that  a  large  part,  and  in  some  cases  all,  of  the 
stimulus  of  use,  is  only  sufficient  for  the  maintenance 
of  the  organism  in  working  condition,  and  that  there  is 
no  surplus  to  be  expended  in  progressive  evolution. 

It  is  however  true  that  some  organs  are  stimulated 
to  excessive  growth  by  active  use.  Such  are  some  of 
the  teeth,  which,  if  not  worn  at  the  crown  by  the  op- 
position of  those  of  the  opposite  jaw,  soon  grow  to  an 
inconvenient  length.  This  occurs  in  the  hypsodont 
molars  of  horses  and  artiodactyles,  and  in  the  pris- 
matic molars  and  incisors  of  Glires.  Hypsodonty  in 
general  is  an  illustration  of  continuous  growth  induced 
by  long-continued  stimulus  in  those  orders  of  Mam- 
malia, and  in  the  Toxodontia  and  Proboscidia.  The 
excessive  growth  of  the  canines  in  the  South  American 
saber-tooth  tiger,  and  of  the  incisors  of  the  mammoth, 
are  cases  where  the  energy  of  growth  has  not  subsided 
in  time  to  prevent  excess. 


KINETOGENESIS.  383 

Several  years  ago  Prof.  August  Miiller  and  I  called 
attention  nearly  simultaneously  to  the  probability  that 
many  of  the  forms  of  the  reproductive  organs  of  plants, 
especially  the  flowers,  are  due  to  the  strains  and  other 
effects  produced  by  their  use  by  insects.  Rev.  George 
Henslow  has  written  a  book  in  which  this  subject  is 
set  forth  in  detail.1  It  is  impossible  to  demonstrate 
this  point  with  the  same  certainty  as  the  kinetogenetic 
origin  of  the  articulations  of  the  vertebrate  skeleton 
and  their  characters,  owing  to  the  absence  of  paleon- 
tologic  evidence.  Henslow,  however,  says:  "When 
we  find  innumerable  coincidences  all  tending  in  one 
direction,  coupled  with  an  indefinite  capacity  for  vary- 
ing in  response  to  forces  in  all  parts  of  plants,  I  still 
maintain  that  [this]  theory  does  not  utterly  break 
down,"  as  asserted  by  Mr.  Wallace.2  Wallace  argues 
that  since  many  regular  flowers  have  been  subject  to 
the  irritation  of  insects  and  have  not  become  irregu- 
lar, there  is  no  reason  to  suppose  that  this  is  the  cause 
of  the  irregularity  in  question.  To  this  Henslow  re- 
plies:3 [Mr.  Wallace]  "will  see  that  existing  regular 
flowers  being  mostly  terminal,  have  no  lower  petals  at 
all,  but  are  so  situated  as  to  offer  access  to  insects 
from  all  points  of  the  compass.  Moreover,  when  a 
plant  with  normally  irregular  flowers  (which  are  always 
situated  close  to  the  axis,  so  that  insects  can  only  en- 
ter them  in  one  way)  produces  a  blossom  in  a  terminal 
position  (as  foxglove,  larkspur,  horse-chestnut,  etc., 
often  do),  it  at  once  becomes  quite  regular."  This 
change  may  be  brought  about  artificially,  for,  says 

]  The  Origin  of  the  Floral  Structures  by  Insect  and  Other  Agencies.     Inter- 
national Science  Series,  Vol.  LXIV. 
^Natural  Science,  1894,  p.  178. 
^Natural  Science,  1894,  p.  262. 


384    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

Henslow,  "flowers  normally  irregular  in  nature  often 
revert  to  their  ancestral  regular  forms  under  cultiva- 
tion in  the  absence  of  insects,  and  then  come  true  from 
seed,  as  the  Gloxinias," 


CHAPTER  VII.-NATURAL  SELECTION. 


ATATURAL  SELECTION  is  the  process  of  dis- 
1M  crimination  of  variations,  by  which  those  which 
are  most  in  harmony  with  the  environment  survive.  It 
is,  in  short,  as  expressed  by  Spencer,  "the  survival  of 
the  fittest."  Fitness  is  of  various  kinds,  and  is  only 
determined  by  the  nature  of  the  environment.  The 
success  of  a  variety  which  appears  in  aquatic  sur- 
roundings will  depend  on  characters  different  from 
those  which  bring  success  in  a  forest.  Variations 
which  favor  survival  and  increase  among  carnivorous 
animals  differ  from  those  useful  to  the  life  of  herbivo- 
rous forms.  So  survival  in  human  society  depends  on 
characters  different  from  those  which  secure  the  same 
result  among  the  lower  animals,  etc.  It  is  thus  evi- 
dent that  natural  selection  is  of  many  kinds  and  that 
forms  survive  for  various  reasons  ;  and  it  is  hence  of 
universal  application.  The  reasons  for  survival  may 
be  divided  into  those  which  depend  for  survival  on  the 
relations  of  a  type  to  the  non-living  environment,  and 
those  which  depend  on  the  living.  The  former  may  be 
divided  into  those  which  are  passive  and  those  which 
are  active.  The  particular  influences  may  be  imper- 
fectly enumerated  as  follows : 


386    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

Non-living  environment. 
a.   Passive. 

Isolation  of  areas  ;  continuity  of  areas  ;  building  material ; 

food  ;  place  of  concealment ;  temperature  ;  humidity. 
aa.   Active. 

Pressure  of  earth,  water,  and  air. 
II.  Living  environment. 

Food  ;  reproductive  potency  ;  sexual  selection ;  digestive 
and  other  physiological  power ;  muscular  strength  ;  su- 
perior weapons  and  other  special  mechanisms ;  intelli- 
gence. 

I  have  already  (page  4)  quoted  the  language  of 
Darwin,  where  he  states  that  the  supposition  that  nat- 
ural selection  is  a  cause  of  the  origin  of  variations  is  a 
mistake.  From  the  nature  of  selection,  Darwin's  po- 
sition thus  expressed,  is  self-evidently  sound.  The 
attempt  has,  however,  been  made  to  apply  the  term 
selection  to  the  efficient  cause  of  all  variation,  and  to 
divide  its  exhibitions  into  two  kinds,  natural  and  arti- 
ficial selection.  If  the  primary  assumption  involved 
in  this  position  is  illogical,  the  dual  division  proposed 
is  absurd.  As  may  be  readily  seen  in  the  table  in  the 
preceding  paragraph,  in  which  the  factors  of  natural 
selection  are  enumerated,  the  conditions  necessary  to 
selection  are  mostly  identical,  whether  imposed  by  na- 
ture or  by  the  hand  of  man  ;  i.  e.,  whether  natural  or 
artificial.  The  physiological  effects  of  food,  tempera- 
ture, exercise,  etc.,  do  not  differ,  whether  due  to  nat- 
ural conditions,  or  to  the  influence  of  man.  The  ob- 
servation of  man's  influence  is  indeed  especially  in- 
structive in  increasing  our  knowledge  of  the  effects  of 
natural  causes,  since  in  the  former  case  we  have  the 
process  in  action  within  our  control,  while  in  the  latter 
case  it  is  not. 

The  subject    of   natural   selection   has  been  ably 


NATURAL  SELECTION.  387 

treated  by  Darwin,  Wallace,  and  other  writers,  and  it 
is  one  on  which  much  further  research  may  be  profita- 
bly expended.  It  is  the  science  of  adaptations,  and 
the  name  Chorology  has  been  framed  for  it  by  Haeckel, 
but  the  earlier  term  CEcology  is  now  generally  used.  It 
was  not  overlooked  by  biologists  prior  to  Darwin  and 
Wallace,  and  is  stated  in  general  terms  by  Lamarck  in 
his  Philosophic  Zoologique,  but  it  was  reserved  for  the 
two  authors  just  mentioned  to  create  the  science.  I 
shall  here  only  refer  to  a  few  aspects  of  the  subject. 
Isolation  naturally  tends  to  emphasize  any  pecu- 
liarities of  structure  which  may  harmonize  with  the 
conditions  of  the  environment,  by  the  barrier  which  it 
sets  up  against  the  entrance  and  mixture  of  forms  from 
other  localities  where  the  environments  are  more  or 
less  different,  and  where  the  characters  are  correspond- 
ingly proportionately  diverse.  Isolation  conversely 
prevents  the  emigration  of  forms,  and  the  consequent 
mixture  with  the  differing  forms  of  other  regions. 
Breeding  in  and  in  is  produced  on  a  large  scale.  Geo- 
graphical isolation  is  a  result  of  the  formation  and 
population  of  islands,  whether  this  be  accomplished 
by  submergence  below  or  by  elevation  above  sea  level. 
A  noteworthy  illustration  of  the  former  case  is  seen  in 
the  West  Indian  Islands,  which  represent  the  elevated 
regions  of  a  former  continent.  Here  the  faunae  of  the 
respective  islands  have  been  separated  from  each  other 
since  late  Pliocene  time.  We  find  that  while  most  of 
the  genera  of  land  Vertebrata  are  generally  distributed, 
each  island  possesses  peculiar  species.  This  is  even 
true  of  the  birds,  whose  powers  'of  migration  are  quite 
sufficient  to  enable  them  to  pass  from  island  to  island. 
The  restriction  of  land  mollusca  is  still  greater,  several 
islands  having  genera  peculiar  to  them. 


388    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

Isolation  is  also  produced  by  inequalities  of  land- 
surface,  resulting  from  the  elevation  of  mountain 
ranges,  plateaus,  etc.  This  is  well  seen  in  Mexico 
and  Central  America  where  the  number  of  species  of 
Vertebrata  is  large,  owing  to  the  fact  that  many  of 
them  are  restricted  to  very  narrow  areas  bounded  by 
impassable  barriers.  The  restriction  of  species  of  land 
Mollusca  to  each  of  the  numerous  valleys  of  the  Ha- 
waiian Islands  has  been  made  the  subject  of  an  espe- 
cial study  by  Dr.  Gulick,  who  treats  of  them  with 
especial  reference  to  the  evolution  of  their  forms. 

The  assimilation  of  inorganic  matter  necessarily 
preceded  that  of  organic  matter,  so  that  this  function 
characterized  the  first  organic  beings,  whether  animal 
or  plant-like  in  other  respects.  Among  animals  we 
may  regard  the  vegetable  feeders  as  having  by  a  little 
preceded  the  carnivorous  forms.  Omnivorous  forms 
must  have  come  into  existence  soon  after,  and  from 
these,  both  classes  of  feeders  have  been  from  time  to 
time  recruited  ever  since.  The  primitive  Vertebrata 
were  probably  carnivorous,  and  most  of  the  fishes  and 
Batrachia  have  always  been  such.  Herbivorous  forms 
have  arisen  from  time  to  time  among  Reptilia,  and  of 
granivorous  birds  there  are  many.  The  early  Mamma- 
lia were  divided  between  omnivorous  (Multitubercu- 
lata)  and  insectivorous  types  (Protodonta,  Pantothe- 
ria)  ;  while  the  higher  Mammalia  of  all  kinds  were  de- 
rived from  more  or  less  omnivorous  forms  (primitive 
Condylarthra  and  some  Creodonta).  We  may  account 
primitive  insects  to  have  been  largely  herbivorous,  even 
more  than  they  are  at  the  present  time,  while  Carnivora 
predominate  in  marine  invertebrate  life.  It  is  not  diffi- 
cult to  understand  that  circumstances  of  the  environ- 
ment would  determine  the  food  of  animals,  and  would 


NATURAL  SELECTION.  389 

divert  omnivorous  forms  into  carnivorous  or  herbivo- 
rous habits  as  abundance  of  food  and  competition  of 
rivals  might  dictate. 

Sexual  selection  is  of  two  general  classes,  that  in 
which  the  male  selects,  and  that  in  which  the  female 
determines  the  result.  In  the  former  case  the  most 
vigorous  males,  or  those  in  which  the  mechanisms  for 
seizing  the  females  are  most  effective,  propagate  their 
kind  most  successfully.  It  is  well  known  that  in  many 
animals,  especially  the  Arthropoda,  the  males  are  fur- 
nished with  especial  organs  of  prehension.  In  verte- 
brates similar  organs  are  especially  conspicuous  in 
some  of  the  Batrachia  Salientia.  (See  p.  65.) 

The  species  of  Arcifera  exhibit  peculiar  structures 
during  the  breeding  season  ;  either  an  extension  of  the 
natatory  membrane,  or  the  development  of  corneous 
plates  or  spurs,  as  aids  to  prehension.  There  is  much 
variety  and  efficiency  displayed  in  this  point  (except 
in  Bufonidae),  in  especial  contrast  to  the  apparent  ab- 
sence of  all  but  the  weakest  modifications  among  the 
Ranidae.  This  is  in  compensation  for  the  structure  of 
the  sternum,  whose  lateral  halves,  being  movable  on 
each  other,  offer  a  slighter  basis  of  resistance  for  the 
flexor  and  extensor  muscles  of  the  fore  limbs  of  the 
male.  In  the  Firmisternia  the  halves  of  the  shoulder 
girdle  do  not  overlap  below  on  the  middle  line,  but 
abut  against  each  other,  thus  preventing  compression 
(Fig.  51,  page  198). 

While  no  appendages  of  the  season  have  been  ob- 
served in  some  Cystignathidae,  in  several  genera  two 
acute  spurs  appear  on  the  superior  aspect  of  the  thumb 
and  more  rarely  spur-like  tubercles  on  the  breast ;  the 
body  is  sometimes  shielded  with  hardened  points  on 
the  rugosities,  or  the  lip  surrounded  by  an  arched 


3QO    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

series  of  corneous  rugae.  In  the  Leptodactylus  penta- 
dactylus  Laur.  a  huge  acute  process  of  the  metacarpal 
of  the  thumb,  projects  inwards.  Its  apex  is  covered  by 
a  horny  cap,  and  it  is  a  formidable  grappling-hook  to 
aid  the  male  in  retaining  his  hold.  There  is  added  to 
this  in  the  same  species  a  horny  plate  on  each  side  of 
the  thorax  of  the  male,  from  which  project  three  acute 
points. .  With  these  fixed  in  her  back  and  the  thumb 
spikes  in  her  breast  the  females  cannot  escape.  Struc- 
tures like  this  do  not  appear  in  the  Firmisternia. 
Here  the  inferior  elements  of  the  scapular  arch  abut 
against  each  other,  so  that  the  thoracic  cavity  does 
not  contract  on  pressure,  and  the  possibility  of  the 
male  retaining  a  firm  grip  on  the  female  is  thereby 
greatly  increased.  In  the  Cystignathus  pachypus  the 
males  exhibit  a  permanent  enlargement  of  the  bra- 
chium,  dependent  on  largely  developed  anterior  and 
posterior  alae  of  the  humerus.  (Vide  Giinther,  Ann. 
Mag.  N.  H.,  1859.) 

Another  kind  of  male  selection  is  accomplished  by 
the  combats  of  males  for  the  possession  of  the  females. 
This  is  usual  in  polygamous  birds  and  Mammalia,  and 
in  some  promiscuous  species  of  both.  Of  the  birds  the 
Gallinae  form  the  best  known  example ;  and  of  the 
mammals,  most  Ungulata,  and  the  eared  seals  (Otari- 
idae),  are  illustrations.  In  this  way  the  weak  males 
are  eliminated  either  by  death,  or  by  exclusion  from 
the  opportunity  of  reproduction.  The  males  in  such 
species  are  armed  with  spurs,  horns,  or  large  teeth, 
except  in  some  of  the  Perissodactylaj  which  have 
neither. 

Female  selection  is  seen  in  another  direction.  Here 
the  male  attracts  by  the  superior  brilliancy  of  his  colors 
or  peculiarity  of  physical  appearance,  as  well  as  by 


NATURAL  SELECTION.  391 

his  notions.  The  available  growth-energy  of  the  male 
being  superior  to  that  of  the  female  in  most  animals, 
his  structure  is  more  liable  to  excess  of  development 
in  useless  directions.  In  many  of  the  Arthropoda, 
especially  the  Insecta,  the  males  possess  processes  of 
the  head  and  thorax  besides  the  especially  useful  pre- 
hensile peculiarities  of  the  limbs.  Among  Vertebrata 
the  male  generally  possesses  the  more  brilliant  colors. 
This  is  especially  noteworthy  in  fishes  and  birds.  It 
is  also  frequently  the  case  in  lizards,  although  in  one 
genus  (Liocephalus)  the  female  has  the  brighter  hues. 
The  selection  (taking  no  account  of  the  origin  of  these 
characters)  acts  in  the  probable  preference  by  the 
females  for  the  most  brilliant  colors  and  most  impres- 
sive forms,  thus  propagating  both,  and  in  the  neglect 
of  those  males  in  which  these  characters  are  not  so  well 
developed.  The  plainness  of  the  females  aids  in  their 
concealment  and  enables  them  to  perform  their  ma- 
ternal functions  in  safety. 

The  desire  of  the  males  to  attract  the  favor  of  the 
females  leads  to  many  peculiar  performances  among 
birds.  The  males  display  their  plumage  by  spreading 
their  wings,  tail,  tail-coverts,  etc.,  and  strut  and  go 
through  many  antics  in  the  presence  of  the  females. 
Familiar  examples  are  seen  in  our  barnyards  in  the 
turkeys,  peafowls,  and  pigeons.  In  the  paradise-bird 
the  most  remarkable  exhibitions  occur,  according  to 
Wallace.  In  song-birds  the  male  is  frequently  the  only 
or  the  best  songster,  and  the  development  of  the  vocal 
powers  resulting  from  the  sexual  impulse  is  most  re- 
markable. Among  Mammalia  the  female  selection  is 
less  common  than  male  selection.  In  the  case  of 
some  of  the  old  world  monkeys  (Macacus,  e.  g.)  the 
female  presents  the  greater  physical  indication  of  ex- 


392    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

citement  in  the  extraordinary  development  of  the  nates 
at  the  season  of  heat.  Mankind,  appropriately  to  the 
high  development  of  the  mental  powers,  is  selected 
with  reference  to  qualities  of  mind  as  well  as  with  re- 
gard to  the  physical  attractions.  Mental  advantages 
being  equal,  beauty  is  preferred,  but  beauty  is  often 
neglected  in  favor  of  superior  moral  and  intellectual 
characteristics.  Both  sexes  take  part  in  the  selection ; 
in  the  lower  races  chiefly  the  male,  while  in  the  higher 
races  the  choice  rests  ultimately  with  the  female.  It 
is  probable  that  in  future  civilized  mankind  will  exer- 
cise more  care  than  now  in  the  prevention  of  marriage 
of  persons  affected  with  serious  physical  and  mental 
defects,  such  as  chronic  diseases,  insanity,  alcoholism, 
criminality,  etc. ;  but  beyond  this,  supervisory  selec- 
tion cannot  go.  The  supposition  which  is  sometimes 
entertained  by  some  persons,  that  mankind  will  in  a 
state  of  higher  civilization  prefer  physical  to  mental 
perfection,  is  certainly  ill  founded.  And  among  men- 
tal qualities,  a  high  value  will  always  be  attached  to 
those  which  render  social  life  easiest  and  most  pleasant ; 
the  standards  of  ease  and  pleasure  being  innumerable. 
Among  the  most  conspicuous  examples  of  the  ac- 
tion of  natural  selection  are  to  be  found  those  resem- 
blances in  color  or  form  between  animals  and  their 
environment  which  serve  to  conceal  them  from  ene- 
mies. Animals  possessing  such  protective  appear- 
ances naturally  escape  the  observation  of  enemies 
which  prey  on  them,  while  those  which  do  not  possess 
them  are  more  readily  captured  and  eaten.  Much  is  to 
be  found  of  interest  on  this  attractive  subject  in  the 
writings  of  Wallace,  Poulton,  Beddard,  and  others. 
The  two  authors  first  named  ascribe  these  color  and 
form  characters  to  natural  selection  as  a  cause.  This  is, 


NATURAL  SELECTION.  393 

however,  impossible ;  yet  natural  selection  has  un- 
doubtedly been  the  cause  of  their  survival.  Professor 
Poulton  has  demonstrated  (p.  230)  that  the  protective 
colors  in  lepidopterous  pupae  are  produced  directly 
by  the  influences  of  light  on  the  nerves  of  the  ani- 
mal and  its  reflex  action  on  the  pigment  depository 
process. 

The  first  objection  to  the  belief  that  natural  selec- 
tion is  the  primary  cause  of  organic  evolution  has 
been  already  stated  as  follows :  '  'A  selection  cannot 
be  the  cause  of  those  alternatives  from  which  it  se- 
lects. The  alternatives  must  be  presented  before  the 
selection  can  commence."  But  the  supporters  of  the 
view  that  natural  selection  is  the  origin  of  variation 
allege  that  it  produces  this  result  by  the  continued 
survival  of  minute  differences  which  are'  useful,  thus 
accumulating  variation.  That  minute  advantageous 
differences  will  secure  survival  no  one  can  doubt,  but 
it  must  be  remembered  that  the  variations  which  con- 
stitute evolution  have  been  in  a  vast  number  of  cases 
too  minute  to  be  useful.  But  the  general  question  is 
not  affected  by  the  supposition  that  advantageous  va- 
riations may  be  sometimes  minute.  Minute  or  great, 
they  have  to  be  assumed  in  the  argument  for  selec- 
tion ;  and  whether  minute  or  great,  they  have  a  def- 
inite cause. 

* 
*  * 

In  conclusion  of  Part  II.  of  this  book,  I  trust  that  I 
have  adduced  evidence  to  show  that  the  stimuli  of 
chemical  and  physical  forces,  and  also  molar  motion 
or  use  or  its  absence,  are  abundantly  sufficient  to  pro- 
duce variations  of  all  kinds  in  organic  beings.  The  va- 
riations may  be  in  color,  proportions,  or  details  of  struc- 
ture, according  to  the  conditions  which  are  present. 


PART  III. 


THE  INHERITANCE  OF  VARIATION. 


PRELIMINARY. 


IN  THE  first  section  of  this  book  I  have  endeavored 
to  show  that  variation  of  character  is  not  promis- 
cuous or  multifarious,  but  that  it  is  limited  to  certain 
definite  directions.  That  this  rule  applies  to  all  kinds 
of  characters,  whether  they  are  of  the  less  fundamen- 
tal kind  which  distinguish  species,  or  of  the  more  fun- 
damental kind  which  distinguish  the  higher  divisions. 

In  the  second  section  I  have  endeavored  to  show 
that  many  characters,  both  those  of  the  more  super- 
ficial and  those  of  the  profounder  kinds,  are  the  direct 
result  of  chemical  and  physical  stimuli,  and  of  molar 
motion  or  use,  or  of  the  absence  of  the  latter  or  dis- 
use. 

It  now  remains  to  ascertain  whether  the  characters 
or  variations  so  produced  are  inherited  ;  that  is,  whether 
characters  so  acquired  are  transmitted  to  succeeding 
generations.  Unless  this  proposition  is  demonstrated, 
our  knowledge  of  the  method  of  evolution  remains  in- 
complete, and  we  must  look  for  some  new  explana- 
tion of  the  progressive  increments  and  decrements  of 
structure  which  constitute  the  history  of  organic  life. 
The  present  part  of  this  book  will  be  devoted  to  an 
examination  of  this  question,  and  to  the  exposition  of 
such  laws  as  may  be  derived  from  such  examination. 


CHAPTER  VIII.— HEREDITY. 


i.  THE  QUESTION  STATED. 

IT  IS  the  popular  belief  that  characteristics  of  par- 
ents are  transmitted  to  their  offspring  through  the 
medium  of  the  reproductive  cells.  This  opinion  is 
founded  on  an  infinitude  of  observations  easily  made 
on  plants,  animals,  and  men,  and  in  fact  it  is  not  de- 
nied as  a  general  statement  by  anybody.  It  is  a  fact 
of  ordinary  observation  that  many  and  apparently 
most  of  the  structural  characteristics  of  one  generation 
are  inherited  by  its  offspring.  Not  only  is  this  the 
case,  but  the  functionings  of  organs  which  depend  on 
minute  histological  peculiarities  are  inherited.  Such 
are  points  of  mental  and  muscular  idiosyncrasy;  of 
weakness  and  strength  of  all  or  any  of  the  viscera, 
and  consequent  tendencies  to  disease  or  vigor  of  spe- 
cial organs.  Darwin  has  collected  in  his  work  on  the 
Descent  of  Man  numerous  instances  of  the  inheritance 
of  various  tricks  of  muscular  movement  of  the  face, 
hands,  and  other  parts  of  the  body.  But  it  is  a  fact 
of  equally  ordinary  observation  that  some  peculiarities 
of  parents  are  not,  or  may  not  be  inherited,  and  among 
these  may  be  enumerated  mutilations  and  injuries,  as 
well  as  characters  which  are  normal.  It  is  then  a 
question  of  essential  importance  to  ascertain  what 


HEREDITY.  399 

kinds  of  characters  are  inheritable,  and  what  are  not 
inheritable. 

It  has  been  insisted  by  Weismann  and  others  that 
characters  which  are  newly  acquired  by  an  organism 
are  not  inherited,  whether  they  be  products  of  normal 
or  abnormal  conditions.  In  support  of  this  view,  he 
points  to  the  early  isolation  in  embryonic  life  of  the 
reproductive  cells  from  the  remainder  of  the  organism, 
and  their  continued  isolation  during  later  life,  so  that 
they  are  protected  from  the  stimulating  influences 
which  affect  the  remainder  of  the  body.  He  also 
points  to  the  permanence  of  this  isolation  of  the  germ 
plasma  from  generation  to  generation,  which  insures 
only  the  transmission  of  those  characters  which  it 
contains,  as  distinct  from  those  which  are  found  in 
the  remaining  cells  of  the  organism,  which  constitute 
the  body  or  soma.  The  characters  which  are  inher- 
ited, and  which  are  present  at  birth  are  termed  con- 
genital, while  those  which  appear  in  the  body  under 
the  influence  of  external  stimuli  are  termed  acquired. 
The  theory  of  Weismann  then  is,  that  the  acquired 
characters  are  not  inherited. 

Besides  the  fact  that  sporadic  injuries  and  mutila- 
tions of  the  soma  are  not  inherited,  there  have  been 
cited  various  cases  of  the  non-inheritance  of  mutila- 
tions which  have  been  often  repeated  and  for  long 
periods  of  time.  Thus  the  rupture  of  the  hymen  in 
human  females  has  not  been  followed  by  its  abolition. 
The  practice  of  circumcision  by  the  Jews  has  not  re- 
sulted in  the  disappearance  from  that  race  of  the  por- 
tion of  the  body  thus  artificially  removed.  The  con- 
tinued cutting  of  the  hair  of  men  of  many  races  has 
not  made  it  less  abundant.  The  practice  of  distorting 
the  feet  of  a  class  of  their  women  by  the  Chinese  has 


400    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

not  modified  the  shape  of  that  part  of  the  structure  in 
the  race.  I  have  myself  cut  off  the  tails  of  nine  suc- 
cessive generations  of  mice  without  producing  the 
slightest  effect  on  the  length  of  the  tails  of  the  tenth. 

Nevertheless  such  negative  evidence  only  demon- 
strates that  such  modifications  of  the  structure  may 
not  be  inherited.  A  single  undoubted  example  of  the 
inheritance  of  a  mutilation  would  prove  that  no  in- 
surmountable barrier  to  such  inheritance  exists.  And 
well  authenticated  examples  of  such  cases  are  known 
and  will  be  mentioned  later  on.  But  it  is  not  with 
mutilations  that  the  paleontologist  has  to  do.  The 
rupture  of  the  hymen  and  circumcision,  and  most  muti- 
lations, can  only  occur  once  in  the  life  of  the  individual, 
and  generally  they  produce  no  appreciable  direct  effect 
on  his  or  her  metabolic  physiology.  Moreover,  the 
mutilations  above  cited  as  not  inherited  are  experi- 
enced by  but  one  sex,  except  in  the  case  of  the  tails 
of  the  mice.  The  question  is  widely  different  with  re- 
gard to  the  parts  of  the  structure  in  which  we  observe 
the  real  differences  between  organic  types.  The  defi- 
nitions of  natural  divisions  rest  to  a  great  extent  on 
the  diversities  displayed  by  the  organs  of  motion  and 
nutrition.  Now  these  are  in  use  in  animals  during 
most  of  the  hours  not  spent  in  sleep.  Their  move- 
ments are  perpetual,  and  their  activities  only  cease 
with  death.  It  is  then  quite  unreasonable  to  cite  the 
history  of  mutilations  as  evidence  against  the  inheri- 
tance of  natural  characters  produced  by  oft-repeated 
and  long  continued  natural  causes. 

It  has  been  shown  in  Part  Second  of  this  book  that 
structural  characters  are  produced  by  use  and  other 
stimuli  to  growth.  It  has  also  been  shown  in  Part 
First  that  the  characters  so  produced  show  a  progres- 


HEREDITY.  401 

sive  increment  or  evolution  from  earlier  or  later  geo- 
logic periods.  There  are  two  possible  explanations 
of  this  phenomenon.  The  one  is  that  the  characters 
of  one  generation  are  inherited  by  the  next,  which 
adds  to  them  by  the  activity  of  the  same  stimuli  which 
gave  them  origin,  thus  producing  progressive  increase 
of  growth.  The  alternative  is,  that  these  structural 
characters  are  produced  by  each  generation  for  itself. 
It  is  obvious  that  the  latter  hypothesis  provides  for 
no  additional  development  of  a  character  in  one  gen- 
eration above  another.  There  are  other  objections  to 
the  latter  view,  but  letting  these  pass  for  the  present, 
it  is  only  necessary  to  examine  the  embryonic  history 
of  animals  to  show  that  it  is  entirely  untenable.  For 
if  some  or  all  of  these  acquired  characters  can  be 
found  present  in  the  early  stages  of  growth,  as  in  the 
egg,  the  pupa,  the  foetus,  etc.,  it  becomes  clear  that 
such  acquired  characters  have  been  inherited.  That 
such  is  the  fact  is  abundantly  demonstrated  by  embryo- 
logical  researches.  This  fact  alone  is  sufficient  to  set 
at  rest  by  an  affirmative  answer  the  question  as  to  the 
inheritance  of  acquired  characters.  And  that  this 
answer  applies  to  all  time  and  to  all  evolution  is  made 
evident  by  the  fact,  which  is  disclosed  by  paleontology, 
that  all  characters  now  congenital  have  been  at  some  per- 
iod or  another  acquired. 

2.  EVIDENCE  FROM  EMBRYOLOGY. 
a.    Vertebrata. 

I  have  already  (p.  292)  pointed  out  the  gradual 
evolution  through  mechanical  causes  of  the  tongue  and 
groove-joints  in  the  Mammalia  as  exhibited  by  the 
distal  ends  of  the  metapodial  bones  of  the  feet  where 


402    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

they  articulate  with  the  phalanges.  Mr.  Carey  having 
agreed  with  me  that  those  have  been  produced  by  me- 
chanical causes,  he  alleges  that  they  are  not  inherited, 
but  are  produced  by  each  generation  for  itself.  To 
this  Dr.  J.  L.  Wortman  remarks  as  follows  : 

1 '  With  reference  to  Mr.  Carey's  first  proposition 
that  the  metapodial  crests  are  produced  during  the  life 
of  each  individual  by  the  necessary  interaction  of  parts, 
it  appears  to  me  to  be  a  very  simple  one  indeed.  If 
they  are  produced,  by  pressure  during  the  lifetime  of 
each  individual,  and  are  not  inherited,  then  clearly  we 
should  find  the  crests  absent  in  new  born  animals  that 
had  never  walked,  and  in  which  the  metapodials  had 
not  been  subjected  to  any  impact  or  pressure  what- 
ever. I  have  taken  the  trouble  to  examine  a  number 
of  such  examples  in  which  the  distal  ends  of  the  bones 
were  entirely  cartilaginous,  and  I  find  that  the  keels 
and  grooves  are  as  well  developed  as  they  are  in  the 
adult  animal.  I  will  cite  one  case  in  particular  in 
which  I  happen  to  know  the  history  completely.  Dur- 
ing the  past  winter,  a  young  hippopotamus  was  born 
in  the  Zoological  Gardens  in  Central  Park,  New  York, 
and  it  was  stated  to  have  been  a  premature  birth  ;  the 
animal  lived  but  twenty-four  hours,  and  I  was  informed 
by  the  keeper  that  it  never  stood  upon  its  feet.  An 
examination  of  the  feet  shows  that  the  distal  ends  of 
the  metapodials  are  entirely  cartilaginous,  and  in  them 
the  keels  are  as  well  prefigured  in  cartilage  as  they  are 
formed  in  bone  in  the  adult  animal.  I  have  also  found 
the  same  to  be  true  of  new-born  rabbits  and  guinea- 
pigs.  In  another  case  of  a  young  buffalo  calf  preserved 
in  the  American  Museum  Collection,  the  distal  keels 
of  the  metapodials  are  complete  notwithstanding  the 
fact  that  the  epiphyses  of  all  the  bones  are  very  im- 


HEREDITY.  403 

perfectly  ossified.  This  evidence,  it  appears  to  me, 
effectually  disposes  of  the  question  of  the  production 
of  these  structures  during  the  lifetime  of  the  individ- 
ual. They  are  as  truly  inherited  as  is  the  number  of 
digits  or  any  other  important  organ  in  the  animal  econ- 
omy." 

Such  observations  may  be  repeated  indefinitely. 
Thus  the  astragali  of  the  higher  Mammalia  are  already 
grooved  before  birth,  and  are  not  flat  up  to  that  time 
as  in  their  Puerco  ancestry.  The  reduction  of  digits 
appears  very  early  in  foetal  life,  and  the  ball  and  socket 
articulations  of  the  cervical  vertebrae  of  the  Diplarthra 
are  by  no  means  introduced  after  birth. 

The  teeth  possess  the  normal  structure  of  their 
crowns  while  yet  in  the  alveoli  before  eruption.  In 
some  cases  the  transition  from  a  primitive  to  a  modern 
type  of  tooth  has  been  observed  to  take  place  in  the 
embryo. 

Dr.  A.  von  Brunn1  has  shown  that  in  the  embryos 
of  the  rat,  the  enamel-producing  epithelial  layer  of  the 
molar  teeth  undergoes  a  remarkable  change  at  the 
places  where  the  transverse  crests  of  the  crowns  are 
to  appear.  Before  the  enamel  layer  is  deposited,  the 
portion  of  the  epithelial  layer  corresponding  to  the 
cross-crests  undergoes  degeneration,  as  a  result  of 
which  it  acquires  the  character  of  a  stratified  squamous 
epithelium.  Thus  no  enamel  is  laid  down  on  the  sum- 
mits of  the  cross-crests,  which  present  the  exposed 
dentine  when  erupted.  Now  it  is  a  fact  that  the  crowns 
of  the  molar  teeth  of  the  ancestors  of  the  genus  Mus, 
were  covered  with  enamel  at  maturity,  like  all  other 


1 "  Notiz  uber  unvollkommene  Schmelzentwickelung  auf  den  Mahlzahnen 
der  Ratte,  Mus  decumanus  ' ' :  Archi*>fiir  Mikroskopische  Anatomte,  1880,  XVII, 
pp.  241-243,  PI.  XXVII.  Ryder,  American  Naturalist,  1888,  p.  547. 


404    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

primitive  Glires.  The  removal  of  the  enamel  from  the 
apices  of  the  tubercles  and  crests  of  their  descendents 
is  due  to  the  abrasion  consequent  on  ordinary  use. 
On  this  Ryder  (/.  *•.)  remarks  :  ' '  The  great  value  which 
is  to  be  attached  to  the  fact  that  abrasions  of  the 
enamel  of  the  adult,  which  have  reacted  upon  the 
functional  activity  of  the  enamel  organ  of  the  embryo 
rat,  so  that  such  mechanically  induced  alterations  could 
be  inherited,  does  not  consist  so  much  in  the  proof  it 
affords  that  mutilations  can  be  inherited,  as  it  does 
that  mutilations  incurred  in  the  ordinary  struggle  for 
existence,  may,  under  certain  conditions  in  certain 
practically  feral  species,  be  transmitted." 

Having  shown  by  these  examples  that  acquired 
characters  can  be  inherited,  I  offer  some  other  illus- 
trations which  are  at  hand. 

b.   Arthropoda. 

It  has  been  already  rendered  probable  if  not  certain 
(p.  268)  that  the  segments  of  the  body  and  limbs  of  the 
Arthropoda  were  originally  produced  by  the  movements 
of  definite  tracts  on  each  other,  during  the  period  that 
the  external  surfaces  were  becoming  hardened  by  chi- 
tinous  or  calcareous  deposits.  It  is  well  known  that  this 
segmentation  is  no  longer  produced  by  this  mechanical 
cause  during  the  adolescent  or  any  other  post-embry- 
onic stage  of  the  life  of  the  individual,  but  that  it  ap- 
pears during  the  various  stages  of  embryonic  life,  and 
is  therefore  inherited.  Thus  segmentation  of  the  body 
appears  in  the  embryo  while  still  attached  to  the  yolk. 
During  the  larval  life  of  many  insects  the  process  of 
segmentation  is  suspended,  but  during  the  repose  of 
pupal  life,  it  goes  on  with  great  rapidity.  In  this  stage 
while  protected  from  external  mechanical  stimuli,  the 


HEREDITY.  405 

limbs  with  their  specialized  segments  are  fully  devel- 
oped, so  that  the  individual  is  mature  as  it  issues  from 
its  prison.  This  illustration  of  inheritance  derives  its 
point  in  the  present  connection  from  the  fact  that  it 
presents  an  example  of  the  inheritance  of  characters 
which  were  plainly  acquired  by  mechanical  stimuli 
during  post-embryonic  life  of  the  primitive  ancestors 
of  the  Arthropoda. 

3.  EVIDENCE  FROM  PALEONTOLOGY. 

a.    The  Impressed  Zone  of  the  Nautiloids. 

I  have  already  quoted  Professor  Hyatt  on  the  par- 
allelism which  is  characteristic  of  the  various  series  of 
nautiloid  Cephalopoda,  as  discovered  by  paleontologic 
research.  (P.  182.)  The  impressed  zone  is  a  character 
which  has  been  produced  by  mechanical  causes  (pres- 
sure), and  Prof.  Hyatt  has  observed  cases  where  this 
acquired  peculiarity  has  been  inherited  in  instances 
where  the  mechanical  cause  which  produced  it  no  longer 
existed.  He  describes  these  instances  as  follows  i1 

"The  characteristic  dealt  with  in  the  paper  of 
which  this  is  an  abstract,  is  of  essential  importance 
among  nautiloids  and  ammonoids  or  all  of  the  Cepha- 
lopoda having  chambered  shells  and  living  within  their 
shells.  It  consists  mainly  of  an  impression  made  on 
the  inner  side  or  dorsum  of  each  outer  whorl  during 
the  coiling  up,  as  the  whorl  grows  and  is  moulded  over 
the  venter  or  outer  side  of  the  next  inner  whorl. 

"This  matter  will  be  better  understood,  if  a  short 
description  is  given  of  the  following  figures.  Fig.  115 
shows  an  almost  complete  fossil  cast  of  a  full  grown 

I  American  Naturalist,  1893.  October,  p.  865.     Professor  Hyatt  has  person- 
ally looked  over  and  corrected  these  quotations. 


406    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION, 

Metatoceras  cavatiformis  Hyatt,  and  some  of  the  lines 
or  sutures  made  in  the  external  surface  of  the  cast  by 
the  intersections  of  the  partitions  or  septa  that  cut 
up  the  coiled  tube  of  the  living  shell  into  air  cham- 
bers. Fig.  116  shows  a  broken  specimen  of  the  same 
species,  but  with  the  outer  and  older  whorls  in  large 
part  removed.  The  innermost  septum  near  the  center 
of  the  coil  was  built  across  the  interior  after  the  animal 
had  constructed  the  hollow  apex  or  point.  It  then 
moved  along,  adding  to  the  external  wall  of  the  tube, 


Fig.  115. 

which  has  been  destroyed  and  removed  from  this  cast, 
and  built  the  second  septum,  and  so  on  until  it  reached 
the  tenth  septum.  By  some  freak  of  fossilization  a 
number  of  the  septa  beyond  this  have  been  destroyed, 
so  that  if  we  were  to  remove  the  fragment  of  the  ex- 
ternal whorl  and  take  out  the  center  which  has  just 
been  described,  this  would  have  the  exact  aspect  of  a 
cast  of  a  young  shell  with  ten  air  chambers.1  The 


IThe  shaded  area  in  the  center,  shaped  like  a  large  inverted  comma,  was 
an  open  space  in  the  living  shell.    This  is  almost  invariably  filled  by  the 


HEREDITY. 


407 


eleventh  air  space  or  chamber  being  open  and  without 

divisions  would  then  appear  to  be  the  living  chamber 

which  the  animal  occupied  when  it  built  the  tenth  sep- 

t 


Is— 


Fig.  116. 

turn.  Normally  the  shell  really  continued  to  progress 
from  the  tenth  septum  by  additions  to  the  outer  wall 
and  put  in  new  septa  behind  it,  together  with  the  con- 


Fig.  117. 

necting  tube  until  it  reached  s',  and  finally  the  las* 
septum,  Is.  This  one,  Is,  was  really  the  last  one  built 

rocky  matrix  in  which  the  shells  occur  and  is  often,  as  in  this  specimen,  al- 
lowed to  remain.  See  also  4,  5,  6,  of  Fig.  119,  which  show  the  comma  shaped 
umbilical  perforations  or  openings  left  at  the  center  through  the  crytoceran 
form  of  the  young. 


4o8    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


and  it  formed  the  floor  of  a  true  living  chamber,  U, 
formerly  occupied  by  the  animal  at  the  time  of  its 
death  and  burial  in  the  sediment  of  the  carboniferous 
period.  Fig.  115  shows  a  similar  fossil  but  with  a 
longer,  although  still  incomplete  living  chamber.  If 
the  external  wall  of  shell  had  been  preserved  none  of 
these  structures  could  be  seen.  Fig.  117  shows  a  fossil 

Temnochilus  crassus,  a  shell 
of  the  same  family,  with  this 
external  wall  preserved,  and 
all  these  internal  structures 
covered  up.  The  impressed 
zone  is  the  reentrant  curve 
shown  in  all  these  figures 
and  especially  marked  in 
the  lower  outline  of  an  outer 

whorl  of  another  carboniferous  species,  Metacoceras 
dubium  Hyatt,  Fig.  118,  im.  z. 

"It  is  not  necessary  to  go  into  a  discussion  of  the 
details  of  internal  structures  and  their  relations  to  the 
impressed  zone  in  this  abstract,  but  it  is  essential  to 
give  a  general  description  of  the  morphogeny  of  the 
order  of  nautiloids. 

"This  group  of  chambered  Cephalopods  contains 
the  following  classes  of  forms  :  first,  straight,  conical 
shells,  type  Orthoceras,  Fig.  119,  No.  i;  second,  curved 
cones,  Cyrtoceras,  Fig.  119,  No.  2  ;  third  loosely  coiled, 
open  whorled  cones,  do.,  No.  3;  fourth,  coiled  cones 
with  the  whorls  more  or  less  enveloping,  do.,  No.  5. 
The  fourth  and  fifth  forms  are  usually  included  in 
the  old  genus,  Nautilus.  Practically,  it  is  better  to 
designate  the  first  class  as  orthoceran,  the  second  as 
cyrtoceran,  the  third  as  gyroceran,  and  the  fourth  and 
fifth  as  nautilian.  In  tracing  genetic  series  through 


HEREDITY.  409 

? 

time  they  are  found  to  diverge  in  their  evolutibn,  start- 
ing with  the  orthoceran  and  passing  through  jteirallel 
lines  of  forms,  many  of  the  genetic  series  havrng  in 
succession  cyrtoceran,  gyroceran,  and  even  nautilian 
forms  of  the  fourth  and  fifth  classes.  Others,  are  not 
so  perfectly  parallel,  stopping  short  with  the\  cyrto- 
ceran class  of  forms  or  the  gyroceran.  Many  also 
begin  with  cyrtoceran  shells,  while  others  diverge  from 
the  gyroceran,  and  still  other  series  have  only  nautilian 
shells  of  different  grades  of  close  coiling  and  m\olu- 
tion. 

''The  application  of  the  law  of  repetition  in  here 
ity  to  the  chambered  shell-covered  cephalopods,  shows 
that  the  straight  orthoceran  shells,  Fig.  119,  No.  i, 
were  repeated  in  the  young  of  the  curved  cyrtoceran 
forms,  Fig.  119,  No.  2,  and  these  forms  in  their  turn 
in  the  young  of  the  gyroceran  forms,  Fig.  119,  No.  3  ; 
and  this  may  be  seen  by  comparing  the  young  or  api- 
cal part  of  each  shell  represented  in  outline  with  the 
full-grown  shells  of  the  preceding  figures.  The  apex 
of  No.  2,  with  the  whole  of  No.  i  ;  the  apex  of  No.  3, 
with  the  whole  of  No.  2.  It  will  be  understood,  of 
course,  that  the  figures  in  outline  represent  full-grown 
shells,  except  when  otherwise  explained,  and  that  they 
were  built  like  the  shells  of  Nos.  1-2,  by  an  animal 
living  in  their  interiors  and  adding  band  after  band  of 
shelly  matter  to  the  exterior,  but  in  these  outlines  the 
shell  is  supposed  to  be  perfect  and  the  internal  struc- 
tures concealed.1  The  young  of  Fig.  119,  No.  4, 
which  represents  the  fourth  class  of  forms  repeats  the 
cyrtoceran  form,  then  curves  more  closely,  and  just 
before  it  comes  in  contact  there  is  a  short  time  when 

1  Except  in  No.  9,  in  which  a  portion  of  the  shell  is  broken  away,  showing 
the  cast  of  the  interior  and  the  sutures. 


V/sOi 


Fig.  119.— Hyatt  on  Cephalopoda. 


HEREDITY.  411 


EXPLANATION  OF  FIG.  119. 

LETTERING. 

a.  Apex  of  shell.  This  usually  bears  a  scar  on  the  point,  as  shown  in 
Nos.  14  and  15,  but  this  has  no  bearing  on  the  question  discussed,  and  has 
not  been  described.  This  also  represents  the  youngest  (nepionic)  or  cyrto- 
ceran  stage  in  the  growth  of  the  shell,  No.  8  being  a  young  shell  with  complete 
living  chamber.  This  letter  also  indicates  the  location  of  the  sections  corre- 
spondingly lettered  in  the  figures. 

b  is  used  to  indicate  the  section  of  the  cyrtoceran  stage  in  Nos.  11-13. 

b'  is  used  to  indicate  the  place  of  the  sections,  Nos.  4-5^',  upon  the  whorls 
of  Nos.  4-5.  They  were  taken  through  the  whorl  in  the  gyroceran  stage. 

c  is  used  for  the  adolescent  fneanic)  stage  of  growth  in  the  whorl  and  the 
corresponding  sections. 

c'  is  used  for  the  full-grown  (ephebic)  stage  in  the  growth  of  the  whorl  and 
the  corresponding  sections. 

dior  the  first  part  of  the  senile  (gerontic)  stage. 

e  for  the  final  and  most  degenerative  part  of  the  senile  stage. 

iz  for  the  impressed  zone. 

v  venter  or  outer  side  of  the  shell,  the  dorsum  being  the  inner  side  of  the 
whorl. 

•w  for  the  whorls,  thus  i  w  in  Nos.  3  and  4  means  the  end  of  the  first  whorl, 
zwMhe  beginning  of  the  second  whorl,  3  w  that  of  the  third  whorl.  These 
letters  serve  to  show  the  progressive  increase  in  numbers  of  the  whorls  in  the 
different  classes  of  forms. 

FIGURES. 

No.  i.  Outline  of  an  orthoceran  shell. 

No.  2.  Outline  of  cyrtoceran  shell. 

No.  3.  Outline  of  gyroceran  shell. 

No.  4.  Outline  of  nautilian  shell,  having  a  larger  umbilical  perforation 
at  (a)  and  fewer  whorls  at  the  same  age,  than  in  No.  5  ;  in  other  words,  it  is 
less  tightly  and  completely  coiled  up  than  the  class  of  shells  represented  by 
that  figure. 

No.  5.  A  nautilian  shell  with  tighter  coils  than  in  No.  4  and  the  whorls 
coming  in  contact  and  the  impressed  zone  beginning  at  an  earlier  stage. 

No.  6.  Barrandeoceras  bohemicum  (sp.  Barrande)  Hyatt,  showing  the  most 
involute  of  the  Silurian  shells  so  far  as  known ;  No.  6  is  reduced  in  size,  but 
the  section  No.  7  is  natural  size. 

No.  8.  A  young  shell  of  the  same,  natural  size,  with  complete  living 
chamber. 

Nos.  9-10.  Coloceras  globatum  (sp.  De  Koninck)  Hyatt,  adult.  No.  9  has 
a  part  of  the  outer  shell  broken  off,  showing  the  edges  of  the  septal  partitions 
(sutures)  as  lines  on  the  strong  cast  of  the  interior. 

Nos.  11-13.  Same  to  show  the  cyrtoceran  stage  and  section,  with  its  im- 
pressed zone. 

No.  14.  Cenoceras  clausum,  Hyatt. 

Nos.  15-16.  Nautilus  pompiiius,  to  show  the  cyrtoceran  stage  with  its  im- 
pressed zone. 


4i2    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

it  overlaps  the  ,apex  without  touching  it.  At  this  time 
it  is  plainly  gyroceran,  like  the  whole  of  No.  3.  After 
it  touches  the  first  whorl  just  beyond  the  apex  it  re- 
mains in  contact,  and  the  inner  side  or  dorsum  of  the 
second  or  overlapping  whorl  begins  to  show  a  flatten- 
ing as  a  result  of  this  collision  of  the  whorls.  The  sec- 
tions of  the  orthoceran,  cyrtoceran,  and  gyroceran 
whorls  show  no  such  flattening  in  any  of  the  speci- 
mens examined,  although  hundreds  of  different  kinds 
have  been  studied.  The  sections  are  designated  on 
the  plate  by  the  same  letters  as  the  supposed  lines  of 
the  sections  made  through  the  tube,  and  although  dia- 
grammatic figures,  they  give  a  sufficiently  clear  gen- 
eral explanation  of  the  facts  observed.  More  specific 
figures  could  have  been  given  in  abundance  and  will 
be  given  in  the  paper  now  in  course  of  preparation.1 

"Fig.  119,  No.  5,  shows  the  same  phenomena  as 
No.  4.  The  young  is  at  first  cyrtoceran  like  the  adult 
whorl  of  No.  2,  and  open,  then  becomes  gyroceran  in 
curvature  and  finally  overlaps  the  apex  when  it  has 
arrived  at  the  end  of  the  first  volution,  but  does  not  at 
first  touch  it.  Then  coming  into  contact  it  acquires  a 
flattened  area  or  faint  impressed  zone  on  the  dorsum 
or  inner  side  of  the  second  volution,  as  is  shown  in 
the  section  No.  5^.  This  is  similar  to  the  section  of 
No.  4  shown  in  No.  4*:',  which  represents  a  cut  through 
an  adult  whorl  of  the  fourth  class  of  forms.  It  differs 
only  in  being  smaller,  on  account  of  the  younger  stage 
of  growth  at  which  it  occurs. 

"The  entire  series  of  forms  from  orthoceran  to  nau- 
tilian  is  more  or  less  represented,  even  in  the  earliest 
period  at  which  the  nautiloids  appear,  namely,  in  the 

ISee  "Phylogeny  of   an  Acquired  Characteristic,"   Hyatt,   Proceed  tugs, 
American  Philosophical  Society,  Philadelphia,  XXXII.,  No.  143. 


HEREDITY.  413 

rocks  of  the  Quebec  group.  There  is,  however,  this 
qualification :  the  fifth  class  of  forms,  or  the  involute 
nautilian,  are  relatively  rare  and  become  more  abun- 
dant in  successive  periods.  The  young  of  nautilian 
shells  of  the  earlier  periods  are  also  apt  to  be  less  closely 
coiled,  or,  in  other  words,  remain  open  and  similar  to 
cyrtoceras  for  a  longer  time  during  their  growth.  This 
is  shown  by  the  large  size  of  the  central  hole,  or  um- 
bilical perforation,  left  in  the  center  of  full-grown 
shells.  This  perforation  is  much  larger,  as  a  rule,  in 
Paleozoic  than  in  the  Mesozoic  forms. 

''In  each  period  the  genetic  series  or  groups  of  nau- 
tilian forms  have  peculiarities  of  structure  in  the  su- 
tures, ornaments,  apertures,  etc.,  by  which  they  can 
be  separated  from  each  other,  and  these  peculiarities 
are  the  same  as  those  possessed  by  gyroceran,  cyrto- 
ceran,  and  often  orthoceran  shells  which  occurred  often 
earlier  in  time,  so  that  one  can  trace  each  group  of 
nautilian  shells  back  to  its  ancestors  through  the  par- 
allel stages  of  evolution  above  described.  The  groups, 
in  other  words,  are  parallel  in  their  morphogenesis, 
like  two  individuals  of  the  same  parents  in  their  de- 
velopment from  youth  to  old  age. 

"As  a  general  rule  the  impressed  zone  originates, 
as  described  above,  after  the  whorls  come  in  contact, 
rarely  before  this  time  in  the  growth  of  any  individ- 
uals. Barrandeoceras  is  one  of  the  most  involute  shells 
known  in  the  Silurian,  and  Fig.  119,  No.  6,  gives  a 
true  sketch  of  this  species  ;  No.  7,  shows  a  section  of 
a  full-grown  shell  with  a  decided  impressed  zone,  and 
No.  8  is  the  young.  This  last  is  a  purely  cyrtoceran 
form  with  a  compressed  elliptical  section  like  that  of 
No.  7,  but  no  impressed  zone,  the  inner  side  being 
rounded  like  the  diagram  of  Cyrtoceras,  No.  2.  The 


4i4    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

impressed  zone  is  not  present  in  the  young  of  Ophidi- 
oceras,  the  closest  coiled  of  all  these  forms,  nor  in  the 
young  of  most  species  of  the  Silurian  before  the  whorls 
touch,  and  all  of  the  species  likely  to  present  this  pecu- 
liarity have  been  investigated. 

"The  impressed  zone  is  also,  as  a  rule,  lost  in  the 
oldest  stage  of  the  whorl  of  every  individual  when  the 
whorls  cease  to  continue  to  grow  in  contact.  This 
condition  is  represented  in  the  last  part  of  the  outer- 
most whorl  of  Nos.  4  and  5  in  sections,  Nos.  4*?,  5  <?, 
and  in  the  outlines  of  their  apertures,  which  are  ellip- 
tical. The  sections  represent  cuts  through  the  whorls 
when,  as  is  the  case  in  extreme  age,  these  cease  to  in- 
crease in  size.  As  soon  as  this  senile  contraction  be- 
gins to  occur,  the  sides  shrink,  becoming  narrower, 
the  amount  of  involution  becomes  less,  and  the  im- 
pressed zone  shrinks  in  breadth,  as  shown  in  the  sec- 
tions. When  the  whorl  finally  parts  company  in 
consequence  of  continued  contraction,  the  already 
shrunken  impressed  zone,  Nos.  4^,  $d,  rapidly  dis- 
appears, and  the  apertures  of  such  shells  are  frequently 
as  round  and  free  from  indentations  on  the  inner  as  on 
the  outer  side,  as  is  shown  at  the  free  end  of  Nos.  4 
and  5. 

"In  normally  uncoiled  forms,  usually  named  Litu- 
ites,  when  the  adult  or  young  is  coiled,  and  the  suc- 
ceeding stages,  whether  representing  adults  or  old 
shells,  are  uncoiled,  the  phenomena  are  similar.  The 
impressed  zone  is  lost  after  the  growth  ceases  to  bring 
the  whorls  of  the  shell  into  contact. 

"  The  young  and  the  adults  of  many  of  these  forms 
have  now  been  observed  in  the  earliest  periods,  and  it 
is,  therefore,  obvious  that  during  these  early  times  the 
impressed  zone  must  have  been  a  modification  of  the 


HEREDITY?  415 

whorl  which  took  place  in  consequence  of  the  mechan- 
ical effects  produced  by  close  coiling.  This  charac- 
teristic is  slight  when  the  coiling  is  slight  and  is  de- 
veloped in  precise  proportion  to  the  increase  of  coiling 
or  involution  of  the  whorls,  and,  on  the  other  hand, 
when  through  degeneration  due  to  age,  or  to  other 
causes,  the  whorls  cease  growing  in  contact,  the  im- 
pressed zone  gradually  disappears. 

"Thus  it  generally  appears  preceded  and  accompa- 
nied by  an  observable  tendency  in  the  mode  of  growth 
toward  closer  coiling  and  that  this  tendency  is  quite 
capable  of  producing  the  impressed  zone  can  hardly 
be  denied  with  any  show  of  reason,  since  the-charac- 
teristic  tends  to  disappear  in  proportion  as  the  pressure 
is  relieved  through  the  degeneration  of  the  powers  of 
growth-force  to  continue  the  normal  rate  of  progres- 
sive increase  of  bulk  in  old  or  young  or  prematurely 
degenerate  shells  and  in  uncoiled  whorls  of  all  kinds 
and  all  ages. 

"The  shells  of  Devonian  series  of  nautiloids  have 
also  been  extensively  examined,  especially  in  the  more 
involute  nautilian  forms  of  the  genus  Nephriticeras, 
and  so  far  not  one  has  been  found  with  the  slightest 
indication  of  the  presence  of  an  impressed  zone  in 
the  cyrtoceran  or  gyroceran  stages  of  development. 
In  several  examples  also,  the  disappearance  of  this 
characteristic  has  been  observed  in  the  last  stages  of 
old  whorls.  There  is,  therefore,  every  reason  for  re- 
garding the  impressed  zone  as  a  ctetic  characteristic 
acquired  in  the  later  stages  of  growth  and  not  heredi- 
tary so  far  as  is  known  in  any  shells  of  the  earlier  Pa- 
leozoic periods.1 

1  Certain  exceptions  have  been  found  since  this  was  written,  but  their  evi- 
dence is  purely  negative,  it  is  impossible  to  say  of  them  at  present  whether 


416    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

' l  The  same  statement  may  also  be  made  with  regard 
to  the  majority  of  Carboniferous  shells.  There  is,  how- 
ever, a  notable  exception  in  Coloceras  globbtum  (sp. 
De  Kon.)  Hyatt,  and  very  likely  some  other  species 
of  closely  coiled  nautilian  shells.  In  C.  globatum  of 
Vise",  Belgium,  I  found  in  seven  specimens  that  the 
impressed  zone  appeared  while  the  whorl  was  still  in 
the  cyrtoceran  (or  open)  stage.  Fig.  119,  Nos.  9-10, 
give  outlines  of  the  adult  of  this  species,  and  Nos.  n- 
12,  of  the  young  and  the  zone,  showing  that  the  im- 
pression appeared  long  before  the  whorls  touched  each 
other  and  began  to  assume  nautilian  characters.  Sec- 
tion, No.  13^,  shows  the  impressed  zone  occurring  in 
the  cyrtoceran  stage  while  the  venter  or  outer  side  of 
the  whorl  was  rounded.  Such  facts  admit  of  but  one 
explanation,  namely,  that  in  this  species  the  impressed 
zone  had  become  hereditary  and  was  in  consequence 
repeated  at  an  early  age,  previous  to  the  occurrence 
of  close  coiling  which  usually  produced  it  in  the  ances- 
tral forms  of  the  same  group. 

"There  are  certain  correlative  characters  which 
lead  me  to  think  that  this  is  only  a  partial  statement  and 
perhaps  a  more  complete  and  better  one  would  be  as 
follows  :  that  the  impressed  zone,  together  with  a  pe- 
culiar broadening  out  of  the  dorsum  and  helmet-shaped 
section  of  the  whorl,  and  perhaps  also  certain  forms  of 
sutures  occurred  in  the  early  stages  of  some  Carbonif- 
erous species  before  the  nautilian  stage,  and  conse- 
quently they  must  have  been  introduced  by  heredity 
into  the  development  of  this  species  before  the  ten- 
dency to  close  coiling  had  completed  the  first  whorl. 

the  impressed  zone  appeared  as  a  genetic  character  or  as  a  mechanical  neces- 
sity. Either  view  can  be  taken,  but  the  positive  evidence  is  that  they  are  very 
rare,  and  the  impressed  zone  appears  in  them  as  a  parallel  character  of  dis- 
tinct diverging  series  of  forms. — A.  H. 


HEREDITY.  417 

Thus  these  characters,  although  purely  ctetic  in  origin, 
were  repeated  before  the  usual  conditions  recurred  in 
the  ontogeny  of  this  species  which  had  obviously  and 
repeatedly  produced  them  in  the  nautilian  forms  of  the 
earlier  Paleozoic  and  the  more  generalized  genetic 
series  of  the  Carboniferous.  That  this  species,  Col. 
globatum,  is  a  highly  specialized  species  is  shown  by 
other  characteristics,  especially  the  early  inheritance 
of  a  furrowed  abdomen,  shown  at  v  in  Fig.  119,  No. 
n,  and  a  peculiar  aperture. 

"The  Triassic  period  is  unimportant  in  this  con- 
nection since  it  has  but  few  nautilian  species  that  are 
deeply  involute  and  also  sufficiently  well  known  to 
throw  any  light  upon  this  problem.  All  of  the  true 
orthoceran,  cyrtoceran,  and  gyroceran  forms  diminish 
in  the  Carboniferous  and  disappear  with  the  Trias. 

"The  Jura  contains  a  considerable  number  of  nau- 
tilian shells  of  different  genera  of  which  the  cyrtoceran 
stages  are  sufficiently  well  known.  Cenoceros  aratum, 
of  which  several  specimens  have  been  studied,  shows 
the  impressed  zone  and  correlative  characters  in  this 
stage ;  C.  lineatum  is  the  same  ;  C.  clausum,  same  ; 
C.  intermedium,  same.  Fig.  119,  No.  14,  shows  the 
cyrtoceran  stage  in  a  shell  of  C.  clausum,  with  a  well 
developed  impressed  zone,  /.  z.  Endolobus  is  a  char- 
acteristic Paleozoic  type  and  there  is  a  single  survivor 
of  this  series  in  the  Jura,  End.  (Naut.*}  excavatum  sp. 
D'Orb.  It  is,  therefore,  very  interesting  and  instruc- 
tive to  note  that  this  species  has  the  impressed  zone, 
according  to  D'Orbigny's  figure,  during  the  cyrtoceran 
stage.  This  species  has  a  large  umbilical  perforation 
and  is  slower  in  coiling  up  than  other  Jurassic  species. 
The  evidence  that  the  impressed  zone  and  its  correla- 
tive characteristics  are  inherited  in  most  species  of  the 


4i8    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION, 

Jura  before  the  habit  of  close  coiling  could  have  acted 
upon  the  whorls  so  as  to  produce  this  modification  is, 
therefore  very  general  and  convincing. 

"The  leading  characteristic  of  parallelism  in  all 
genetic  series  of  nautiloids  is,  as  may  be  inferred  from 
the  facts  cited,  a  tendency  toward  closer  coiling  and 
greater  involution  in  the  more  specialized  forms  of 
each  separate  series  and  a  correlative  increase  in  the 
profundity  of  the  impressed  zone.  When  the  impressed 
zone  becomes  inheritable  in  some  closely  coiled,  and 
involute  specialized  shells  of  the  Carboniferous  and 
in  similar  shells  in  all  of  the  genetic  series  of  the 
Jura  this  result  is  also  directly  connected  with  the  ob- 
served fact  of  the  quicker  development  of  the  coiling 
up  tendency  in  the  young  of  these  Jurassic  shells.  This 
is  shown  by  the  small  diameter  of  the  umbilical  per- 
foration in  the  centers  of  the  shells  of  the  Carbonif- 
erous. It  is  also  connected  with  the  fact  that  the  prim- 
itive uncoiled  forms,  orthoceran,  cyrtoceran,  and  gy- 
roceran  shells  begin  to  die  out  in  the  Carboniferous 
and  cease  with  the  Trias  as  mentioned  above. 

"This  demonstration  of  the  characters  that  accom- 
pany progress  in  close  coiling,  enables  me  to  fill  a  gap 
which  occurs  in  the  evidence  during  the  Cretaceous. 
In  this  period  the  existence  of  the  impressed  zone  dur- 
ing the  cyrtoceran  stage  of  individuals  has  not  been 
clearly  established  by  observation  except  in  two  spe- 
cies, a  form  allied  to  Cymatoceras  pseudoelegans  D'Or- 
bigny,  from  Faxoe,and  Cymatoceras  elegansirom  Rouen. 
In  other  shells,  although  a  considerable  number  have 
been  broken  down,  the  state  of  preservation  has  been 
invariably  imperfect.  The  coiling,  however,  in  the 
young  of  all  the  shells  examined  is  notably  more  ac- 
celerated than  in  the  similar  shells  of  the  Jura,  and  the 


HEREDITY.  419 

whorls  broader  and  having  more  specialized  charac- 
teristics correlative  with  closer  coiling  and  the  early 
existence  of  an  impressed  zone.  It  is,  therefore,  fair 
to  infer  that  the  evidence  when  accessible  will  confirm 
the  facts  observed  in  previous  periods.1 

"The  same  arguments  apply  also  to  the  tertiary 
forms  as  far  as  known. 

"The  terminal  members  of  the  nautiloids  are,  of 
course,  the  existing  species.  Nautilus pompilius  and  urn- 
bilicatus  have  been  examined  in  a  considerable  number 
of  specimens,  and  in  all  of  these  the  impressed  zone 
and  correlative  helmet-shaped  whorl  and  broad  flat- 
tened dorsal  side  appears  during  the  cyrtoceran  stage. 
Fig.  119,  Nos.  15-16,  are  outlines  of  the  shell  of  pompi- 
lius during  the  cyrtoceran  stage  exhibiting  the  helmet- 
shaped  whorl,  broad  dorsum,  or  inner  side,  and  its 
impressed  zone,  iz.  Thus,  when  the  whorls  touch,  as 
in  all  the  nautilian  shells  of  the  Carboniferous,  Jura, 
and  Cretaceous,  in  which  the  same  acceleration  of  de- 
velopment also  occurs,  the  whorl  is  already  prepared 
to  become  involute  and  to  mould  itself  more  readily 
and  rapidly  over  the  surfaces  of  the  apex  and  the  side 
of  the  succeeding  whorls.  In  other  words,  heredity 
has  begun  the  work  before  the  whorls  touch,  and  be- 
fore the  deepening  and  enlargement  of  the  impressed 
zone  through  the  pressure  of  close  coiling  is  begun. 
There  are  quite  a  number  of  characteristics  of  the  spe- 
cies of  existing  Nautili  which  lead  to  the  inference 
that  they  are  survivors  of  Jurassic  and  generalized 
Cretaceous  and  Cenozoic  forms ;  the  size  of  the  um- 
bilical perforations,  the  smoothness  of  the  shells,  the 
simplicity  of  the  sutures,  and  so  on.  These  facts  are 

iThis  inference  has  been  fully  sustained  by  subsequent  investigations. — 
A.  Hyatt. 


420    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

of  importance  only  in  so  far  as  they  show  that  the  ex- 
isting Nautilus  does  not  represent  the  acme  of  pro- 
gress of  its  order,  but  is  a  descendant  of  shells  with 
less  complicated  structures  than  many  of  the  genera  of 
the  Carboniferous,  Jura,  and  Cretaceous." 

In  these  cases  it  seems  that  the  mechanically  ac- 
quired impressed  zone  is  inherited  from  the  greater 
part  of  the  soma  where  it  existed  to  a  part  of  the  soma 
of  the  young  where  it  could  not  be  produced  by  me- 
chanical causes,  by  reason  of  the  non-contact  of  the 
parts.  This  acquisition  appears  in  a  few  Carboniferous 
species,  and  then  it  is  present  in  the  cyrtoceran  or 
mesozoid  stage  of  all  the  Jurassic,  Cretaceous,  and 
Cenozoic  species.  Professor  Hyatt,  in  his  "Phylogeny 
of  an  Acquired  Characteristic,"  thus  summarizes  his 
conclusions  : 

"The  facts  and  arguments  brought  forward  seem 
to  justify  the  following  conclusions : 

"i.  The  impressed  zone  is  primitively  a  contact 
furrow,  an  acquired  characteristic  of  the  dorsum  of  the 
whorls  of  nautilian  shells  having  large  umbilical  per- 
forations, which  appeared  either  in  the  ananeanic  or 
metaneanic  (maturing)  substages,  and  rarely  later  in 
their  ontogeny.  There  is  abundant  positive  evidence 
that  in  these  primitive  forms  this  furrow  is  a  purely 
mechanical  result  of  the  nautilian  mode  of  growth,  not 
appearing  in  the  ontogeny  before  contact,  and  either 
partially  or  entirely  disappearing  on  the  free  gerontic 
(senile)  volution. 

"2.  The  impressed  zone  does  occur  independently 
of  contact  on  the  free  dorsum  of  the  paranepionic  (ado- 
lescent) substage  as  a  dorsal  furrow  in  some  close- 
coiled,  highly  tachygenic  (accelerated)  nautilian  shells 
in  the  Quebec  group  and  in  the  Devonian. 


HEREDITY.  421 

"  3.  While  there  is  no  positive  proof  that  the  dor- 
sal furrow  originated  through  heredity  in  the  parane- 
pionic  substages  of  these  nautiloids  of  pre-Carbonife- 
rous  age,  there  is  also  no  satisfactory  evidence  that  it 
originated  in  the  young  of  such  species  as  have  this 
character,  through  purely  mechanical  agencies. 

' '  4.  There  is  positive  evidence  that  the  similar  dor- 
sal furrow  which  also  appears  at  the  same  age  in  the 
young  shells  of  Coloceras  globatum  and  perhaps  Ccelo- 
gasteroceras  canaliculatum  among  Carboniferous  nauti- 
loids can  be  explained  only  when  it  is  considered  as  a 
transmitted,  tachygenetic  (accelerated)  characteristic. 

"5.  This  fourth  conclusion  is  supported  by  the 
presence  of  a  similar  dorsal  furrow  in  the  paranepionic 
(adolescent)  substage  of  the  young  shells  of  all  the 
nautiloids  of  the  Jura,  so  far  observed. 

"6.  The  fourth  and  fifth  conclusions  are  rendered 
still  more  probable  by  the  presence  of  the  dorsal  fur- 
row at  an  earlier  age,  the  metanepionic  substage,  in 
all  of  the  nautiloids  so  far  observed,  from  the  begin- 
ning of  the  Cretaceous,  through  the  Tertiaries,  to  and 
including  the  living  species  of  the  genus  Nautilus.  Its 
presence  on  this  cyrtoceran  volution  in  Cretacic  shells 
can  be  explained  only  when  it  is  considered  as  a  trans- 
mitted, tachygenetic  (accelerated)  characteristic  de- 
rived from  ancestral  nautilian  shells  of  the  Jura,  which 
have  the  same  characteristic  at  a  later  age,  i.  e.,  in  the 
paranepionic  substage. 

"7.  The  first  conclusion  is  also  sustained  by  the 
parallel  phylogeny  of  the  impressed  zone  in  the  ances- 
tral forms  of  the  Ammonoidea,  the  Nautilinidae,  and 
especially  in  the  Mimoceras,  the  radical  genus  of  this 
family. 

"8.   The  fourth,   fifth,   and   sixth  conclusions  are 


422    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION, 

also  supported  by  the  presence  of  a  contact  furrow  on 
the  dorsum  of  the  earliest  age  of  the  conch  in  the  spe- 
cialized and  highly  tachygenic  forms  of  the  Goniati- 
tinae  of  the  Devonian  and  of  all  the  remaining  ammo- 
noids  to  the  end  of  the  Cretaceous. 

"9.  These  cumulative  results  favor  the  theory 'of 
tachygenesis  (acceleration)  and  diplogenesis,  and  are 
opposed  to  the  Weismannian  hypothesis  of  the  sub- 
division of  the  body  into  two  essentially  distinct  kinds 
of  plasm,  the  germ-plasm,  which  receives  and  trans- 
mits acquired  characteristics,  and  the  somatoplasm, 
which,  while  it  is  capable  of  acquiring  modifications, 
either  does  not  or  cannot  transmit  them  to  descend- 
ants. "  {Proceedings  American  Philosophical  Society,  Vol. 
XXXII.,  p.  615). 

4.  EVIDENCE  FROM  BREEDING. 

Under  this  head  I  cite  the  results  of  experience  of 
breeding  of  the  domesticated  Vertebrata.  It  is  here 
that  we  have  had  the  best  opportunity  of  testing  the 
possibility  of  the  inheritance  of  acquired  characters, 
since  the  species  in  question  have  been  the  objects  of 
observation  and  experiment  for  a  long  period  of  time. 
I  especially  avail  myself  of  the  writings  in  this  con- 
nection of  Prof.  Wm.  H.  Brewer,  of  Yale  University, 
President  of  the  Agricultural  Society  of  Connecticut. 
The  result  of  his  long-continued  observations  is  con- 
tained in  a  series  of  papers  in  the  journal  Agricultural 
Science  of  the  years  1892-1893.  He  considers  the  sub- 
ject under  the  following  heads,  viz. :  The  inheritance 
of  characters  which  are  due  to  nutrition  ;  of  those  due 
to  the  exercise  of  function  ;  of  those  due  to  disease  ; 
of  those  due  to  mutilation  and  injuries  ;  of  those  due 
to  habit,  training,  and  education;  of  those  due  to  re- 


HEREDITY.  423 

gional  influences  and  to  a  combination  of  causes  ;  and 
of  those  of  acquired  plasticity  and  adaptation.  I  com- 
mence with  an  example  of  the 

a.   Inheritance  of  Characters  Due  to  Nutrition. 

"One  class  of  '  acquired  characters/  the  transmis- 
sion of  which  by  heredity  is  especially  denied  by  Weis- 
mann,  includes  all  'those  which  are  directly  due  to 
nutrition.' 

"This  denial  strikes  at  the  very  foundation  of  what 
has  heretofore  been  considered  an  essential  factor  in 
the  practical  improvement  of  breeds  as  to  size.  The 
size  attained  by  adult,  healthy  domestic  animals  de- 
pends practically  upon  two  causes — heredity  and  nu- 
trition. Heredity  is  of  course  the  chief  one,  for  no 
amount  of  feeding  will  make  the  Shetland  pony  equal 
the  Norman  horse  in  size  ;  but  whatever  the  heredity, 
the  size  of  the  adult  individual  as  compared  with  the 
average  of  others  of  the  same  breed  depends  usually 
upon  its  food.  The  ultimate  weight  of  the  mature 
animal  varies  of  course  with  the  amount  of  fat  assimi- 
lated, which  may  occur  long  after  maturity  ;  but  the 
size  as  dependent  upon  the  frame,  such  as  the  weight, 
length,  and*  general  proportions,  is  modified  by  the 
quantity  and  quality  of  food  available  during  the  grow- 
ing period  of  early  life.  This  fact  no  one  questions  ; 
and  if  these  acquired  characters  are  in  no  degree  what- 
ever transmitted,  then  certain  practices  of  breeders, 
which  are  founded  upon  the  contrary  belief  are  delu- 
sive and  expensive  mistakes. 

"Practical  breeders  have  hitherto  believed  that 
these  characters  are  to  some  degree  transmitted,  and 
practice  accordingly.  I  have  searched  extensively  the 
writings  of  practical  breeders  to  see  if  I  could  find  a 


424    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

single  one  who  questions  it,  and  I  fail  to  find  even  so 
much  as  an  intimation  of  any  such  belief.  All  the 
recorded  observations  founded  upon  actual  practice 
appear  to  point  the  other  way,  and  consequently  the 
fact  of  partial  transmission  is  assumed. 

"  The  practical  value  given  to  this  factor  is  now 
much  smaller  than  formerly  given,  but  that  it  is  a  fac- 
tor of  some  value  is  universally  assumed. 

"During  the  last  century,  and  early  part  of  this, 
many  graziers  had  a  maxim  that  in  the  profitable  pro- 
duction of  animals  for  slaughter,  '  feed  is  more  than 
breed,'  but  now  both  breeders  and  graziers  know  that 
heredity  or  'breed,'  is  the  more  important.  But  no 
breeder  claims  that  a  breed  is  or  can  be  kept  up  to 
extra  size  by  selection  alone.  This  belief  is  so  uni- 
versal, and  is  apparently  so  grounded  upon  long  and 
extensive  experience,  that  I  cannot  find  there  has  ever 
been  an  attempt  to  increase  the  size  of  any  breed  with- 
out special  attention  to  this  factor,  and  consequently 
conclusive  and  direct  experiment  is  entirely  wanting. 
Positive  proof  either  way  cannot  be  deduced  from  the 
actual  experiments  of  breeders  ;  their  belief  that  feed 
as  well  as  selection  is  necessary,  is  a  deduction  from 
the  observation  of  many  facts  which  bear  upon  the 
question. 

"  In  this  connection  it  must  be  borne  in  mind  that 
all  the  best  breeders  recognize  the  rule  laid  down  by 
Darwin,  that  those  characters  are  transmitted  with 
most  persistency  which  have  been  handed  down 
through  the  longest  line  of  ancestry.  Breeders  do  not 
believe  that  the  characters  acquired  through  the  feed- 
ing of  a  single  ancestor,  or  generation  of  ancestors, 
can  oppose  more  than  a  slight  resistance  to  that  force 
of  heredity  which  has  been  accumulated  through  many 


HEREDITY.  425 

preceding  generations,  and  is  concentrated  from  many 
lines  of  ancestry.  Yet  the  belief  is  universal  that  the 
acquired  characters  due  to  food  during  the  growing 
period  has  some  force,  and  that  this  force  is  cumula- 
tive in  successive  generations.  All  the  observed  facts 
in  the  experience  with  herds  and  flocks  point  in  this 
direction.  It  is  the  same  whether  the  observations  re- 
late to  the  increase  in  the  size  of  breeds,  which  has 
been  brought  about  by  systematic  selection  and  feed- 
ing directed  with  this  special  aim,  or  to  the  local  de- 
velopment of  breeds  under  the  combined  influence  of 
the  food  supply  and  unsystematic  selection. 

"  Where  both  large  and  small  breeds  have  been  in 
process  of  improvement  in  the  same  region  at  the 
same  time  and  with  the  same  kinds  of  food,  liberal 
feeding  along  with  systematic  selection  is  always  prac- 
tised where  an  increase  of  size  is  aimed  at,  and  under- 
feeding during  growth  is  practised  when  it  is  desired  to 
reduce  the  size.  We  have  examples  of  these  going  on 
together  contemporaneously.  Breeding  for  increase 
of  size  is  more  common  than  that  for  reducing,  but  the 
latter  occurs  not  only  in  the  small  fancy  breeds  of 
poultry  and  dogs,  but  even  of  cattle.  When  small  and 
delicate  Alderney  cows  were  a  fashionable  ornament  for 
parks  and  lawns,  some  of  the  most  successful  breeders 
practised  starving  systematically,  and  at  least  one 
eminently  successful  breeder  of  these  animals  so  under- 
fed the  growing  calves  that  it  led  to  legal  interference 
by  a  local  Society  for  the  Prevention  of  Cruelty  to 
Animals. 

"So  far  as  I  know,  all  the  breeds  of  especially 
large  horses,  cattle,  and  sheep  have  originated  in  dis- 
tricts of  abundant  food,  usually  in  fertile  valleys  or  on 
plains,  and  excepting  fancy  breeds  of  poultry  and  pets, 


426    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

all  the  smaller  breeds  have  originated  in  districts  of 
scantier  forage.  This  can  hardly  be  due  to  accident, 
for  it  is  as  true  of  local  varieties  of  wild  animals  under 
natural  selection  as  of  domestic  animals  under  artifi- 
cial selection." 

b.   Inheritance  of  Characters  Due  to  the  Exercise  of 
Function. 

This  class  of  cases  has  an  especial  bearing  on  the 
doctrine  of  kinetogenesis.  We  have  a  very  conspicu- 
ous example  of  such  inheritance  in  the  case  of  the 
evolution  of  the  trotting  horse,  which  is  described  by 
Professor  Brewer  as  follows  : 

"We  have  a  copious  literature  relating  to  the  de- 
velopment of  this  breed,  and  the  '  records '  of  speed 
provide  the  data  for  a  mathematical  history  of  the  rate 
of  progress,  and  also  the  measure  of  amount  of  cumu- 
lative variation  that  has  occurred  up  to  this  time. 
These  data  give  to  this  breed  a  special  interest  for 
scientific  study. 

"The  facts  briefly  stated  are  as  follows  :  Trotters 
had  their  uses  for  ages,  but  fast  trotters  were  not 
wanted  until  the  improvement  in  roads  and  in  wheeled 
vehicles  during  the  last  quarter  of  the  last  century 
caused  an  increasing  demand  for  faster  roadsters  for 
light  draft.  Trotting  is  the  gait  of  traction,  as  run- 
ning is  for  riding,  and  trotting  as  a  sport  sprang  up  in 
nearly  all  the  countries  of  Europe  as  well  as  in  Amer- 
ica so  soon  as  faster  trotters  were  needed  for  the  road. 
Then  trotting-horses  began  to  be  bred,  and  long  be- 
fore the  close  of  the  century  there  were  trotting-stal- 
lions  of  considerable  fame.  There  were  also  recorded 
statements  as  to  the  speed  attained. 

"Lawrence,  a  lover  of  trotters,  in  his  Treatise  on 


HEREDITY.  427 

Horses  (London,  1796),  considered  that  'the  utmost 
speed  of  the  English  trotter '  (which  he  believes  to  ex- 
cel all  others),  to  be  a  mile  in  two  minutes  and  fifty- 
seven  seconds.  During  the  next  twenty  years  there 
were  very  many  recorded  trials  of  speed,  and  a  few  of 
the  best  animals,  both  here  and  in  Europe,  trotted  a 
mile  in  three  minutes,  but  none  in  less  time  than  that 
given  by  Lawrence. 

"  Considering  the  number  of  animals  that  were 
tested,  the  widespread  interest  in  the  matter,  and  that 
these  records  were  the  best  of  both  Europe  and  Amer- 
ica, it  is  fair  to  assume  that  this  was  the  utmost  speed 
actually  attained  by  the  best  trotting-horses  until  after 
1820,  although  some  specific  selection  in  breeding  trot- 
ters had  been  going  on  for  half  a  century,  and  possibly 
much  longer. 

"By  1810,  the  taste  for  trotting  as  a  sport  had  died 
out  in  western  Europe,  but  it  increased  here,  and  in 
1818  it  became  a  recognized  sport  under  specific  rules. 
This  is  practically  the  beginning  of  technical  'trotting 
records '  as  we  now  know  them.  It  soon  became 
fashionable  to  drive  a  single  horse  for  pleasure,  a  so- 
cial factor  in  breeding  that  was  lacking  in  the  Old 
World.  This  created  a  demand  for  trotters,  as  well 
as  increased  the  taste  of  trotting  as  a  sport.  Asso- 
ciations were  chartered  for  the  promoting  of  trotting, 
and  special  tracks  built  for  the  exercising  and  training 
of  trotters. 

"At  the  end  of  1824,  six  years  after  the  first  ac- 
cepted three-minute  record,  the  record  had  fallen  to 
2:34,  a  reduction  of  twenty-six  seconds.  This  great 
reduction  so  rapidly  effected  was,  doubtless,  due  chiefly 
to  better  training,  but  also  in  part  to  special  exercise 
of  function,  in  part  to  heredjty,  and  in  part  to  the 


428    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

larger  number  of  animals  trained.  It  is  not  probable 
that  mere  exercise  of  training  could  materially  further 
increase  this  speed,  for  the  next  ten  years  lowered  the 
record  only  two  and  a  half  seconds,  and  twenty-one 
years  more  passed  before  the  first  2:30  record  in  har- 
ness was  made. 

"By  1848,  the  record  was  lowered  to  2:29^,  and 
we  have  now  a  2:30  class,  with  two  or  three  horses 
technically  in  it,  and  perhaps  half  a  dozen  that  had 
actually  trotted  at  that  speed.  Now  we  began  to  have 
distinctively  trotting  blood,  and  heredity  began  to  tell. 

"The  next  decade  lowered  the  record  five  seconds; 
and  the  next  (ending  in  1868),  lowered  it  seven  and  a 
fourth  seconds  more  ;  there  were  several  horses  in  the 
2:20  class,  and  nearly  one  hundred  and  fifty  in  the 
2:30  list. 

1 '  The  next  decade  lowered,  the  record  four  seconds  ; 
and  the  next  (ending  in  1888),  four  and  a  half  seconds, 
and  the  number  of  2:30  horses  had  increased  to  3,255 
animals.  At  the  close  of  last  year,  the  record  had 
been  further  lowered  half  a  second,  to  2:08^  ;  there 
were  5,908  in  the  2:30  list,  507  in  the  2:20  list,  and 
seven  in  the  2:10  list.  This  is  the  history  for  seventy- 
three  years  of  'records.' 

"  Parallel  with  the  evolution  of  this  breed  has  been 
the  development  of  a  breed  of  pacers.  The  fast  ani- 
mals are  not  so  numerous,  but  the  speed  is  greater, 
and  the  gait,  as  a  fast  gait,  is  more  distinctly  artificial. 
The  instincts  involved  will  be  discussed  in  a  later  pa- 
per ;  here  I  will  notice  only  the  development  of  speed, 
because  that  is  the  direct  and  obvious  result  of  func- 
tional development,  and  because  we  have  mathematical 
data  as  to  the  rate  and  amount  of  actual  evolution. 

"That  the  gain  in  sp^ed  has  been  cumulative,  and 


HEREDITY.  429 

that  for  three-fourths  of  a  century,  that  it  has  gone  on 
along  with  systematic  exercise  of  special  function  in 
successive  generations  of  the  present  fast  trotters,  is 
indisputable  and  very  evident.  Selection  has  doubt- 
less determined  the  proper  correlation  of  the  various 
organs  involved  in  the  special  evolution,  but  the  in- 
crease in  speed  has  only  come  along  with  the  func- 
tional development,  which  was  enhanced  by  special 
exercise  in  the  individuals  of  successive  generations. 
The  cumulative  value  of  this,  if  transmitted,  would  be 
vastly  more  than  enough  to  account  for  all  the  increase 
that  has  actually  occurred,  great  as  that  is.  Viewed 
as  phenomena,  there  is  every  appearance  and  indica- 
tion that  the  changes  acquired  by  individuals  through 
the  exercise  of  function  have  been  to  some  degree 
transmitted,  and  have  been  cumulative,  and  that  this 
has  been  one  factor  in  the  evolution  of  speed.  The 
cumulative  variation  has  been  most  marked  since  we 
have  had  a  2:30  class,  that  is,  since  we  have  produced 
animals  that  are  swift  by  heredity,  and  whose  ances- 
tors, as  well  as  themselves,  have  been  exercised  and 
trained  to  trot.  Studied  as  phenomena,  there  is  not  a 
particle  of  evidence  that  these  special  changes  ac- 
quired by  the  individuals  were  totally  lost  to  each  suc- 
cessive generation,  and  that  all  that  was  '  transmitted 
by  heredity,'  was  a  something  that  did  not  exist  in 
either  parent  or  in  any  ancestor.  There  is  nothing 
whatever  in  the  actual  phenomena  observed  anywhere 
along  the  line  of  this  development  of  speed  that  would 
lead  us  to  even  suspect  that  the  changes  due  to  exer- 
cise of  function  had  not  been  a  factor  in  the  evolution, 
and  there  is  not  a  particle  of  evidence,  other  than  met- 
aphysical deductions,  much  less  proof,  that  it  would 


430    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

or  could  have  gone  on  just  the  same  by  mere  selection 
and  adventitious  variation." 

c.   Inheritance  of  Characters  Due  to  Disease. 

Under  this  head  Brewer  cites  a  well-known  case. 
He  says  :  "The  most  extensive  and  complete  set  of 
experiments  yet  published  on  the  artificial  production 
of  disease  by  mechanical 'injuries  are  those  of  Dr. 
Brown-Sequard  on  the  artificial  production  of  epilepsy. 
This  is  a  disease  which  is  certainly  sometimes  heredi- 
tary and  which  may  also  be  produced  by  art  in  previ- 
ously sound  animals.  He  experimented  with  guinea 
pigs  and  produced  many  artificial  epileptics,  and  by 
breeding  these  he  produced  many  congenital  epilep- 
tics. The  disease  artificially  produced  in  the  parents 
was  transmitted  to  the  offspring  in  numerous  cases. 
The  acquired  characters  in  those  cases  were  certainly 
transmitted  to  the  offspring  and  became  hereditary. 
These  experiments  were  continued  and  repeated  by 
his  assistant  and  pupil  Depuy,  and  the  results  abund- 
antly confirmed.  It  was  shown,  moreover,  that  in 
many  cases  it  was  the  tendency  to  become  epileptic  that 
was  transmitted  rather  than  the  disease  itself.  Just 
as  in  a  great  majority  of  cases  of  strictly  hereditary 
disease  it  is  the  constitutional  tendency  rather  than 
the  disease  itself  that  is  commonly  transmitted. 

"These  experiments  have  now  been  before  the 
world  some  years,  during  which  time  ideas  have  greatly 
changed  as  to  the  causes  of  disease,  and  the  nature  of 
hereditary  tendencies,  but  as  yet  there  are  no  pub- 
lished accounts  of  experiments  indicating  that  those  of 
Brown-Sequard  and  of  Depuy  were  not  carefully  per- 
formed, or  that  the  conclusions  were  illusive.  Medical 
literature  abounds  with  alleged  instances  where  ner- 


HEREDITY.  431 

vous  diseases  acquired  by  parents  through  environ- 
ment have  been  transmitted  in  some  shape  to  children, 
but  this  evidence  is  not  nearly  so  conclusive  as  the  ex- 
perimental proof  cited. 

1 '  In  conclusion  we  may  say  that  the  drift  of  all  the 
collated  observations  on  both  man  and  brute  seem  to 
indicate  that  certain  of  the  changes  produced  in  the 
animal  body  by  disease  are  often  to  some  degree  trans- 
mitted, that  these  may  be  cumulative  and  lead  to  de- 
generation if  not  indeed  to  the  extinction  of  families. 
The  experience  of  breeders  as  well  as  the  observations 
of  medical  men  practically  establishes  the  fact  that  ac- 
quired weakness  and  defects  occurring  in  successive 
generations  may  result  in  truly  hereditary  unsound- 
ness." 

d.   Inheritance  of  Characters  Due  to  Mutilation  and 
Injuries. 

While  characters  of  this  kind  are  relatively  rarely 
inherited,  there  is  little  doubt  that  they  can  be.  Dr. 
Brewer  cites  a  few  cases  for  illustration ;  ' « some  of 
them  have  been  already  published,  others  have  not. 
They  are  not  the  most  striking,  but  are  chosen  because 
they  are  representative. 

"a.  A  mare  in  foal  had  an  eye  seriously  injured  by 
burdocks  entangled  in  the  forelock.  She  suffered  with 
violent  ophthalmia,  and  in  due  time  dropped  a  foal  (a 
filly)  which  had  the  corresponding  eye  aborted.  She 
afterwards  bore  several  normal  foals. 

"(This  case  came  under  the  observation  of  the 
eminent  veterinarian,  Professor  Law  of  Cornell  Uni- 
versity. Papers  American  Public  Health  Association, 
2,  p.  254.) 

"&.   A  game-cock,  in  his  second  year,  lost  an  eye 


432     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

in  a  fight.  Soon  after,  and  while  the  wound  was  very 
malignant  (it  never  entirely  healed),  he  was  turned 
into  a  flock  of  game  hens  of  another  strain.  He  was 
otherwise  healthy  and  vigorous.  A  very  large  propor- 
tion of  his  progeny  had  the  corresponding  eye  defec- 
tive. The  chicks  were  not  blind  when  hatched,  but 
became  so  before  attaining  their  full  growth ;  some  at 
the  time  of  acquiring  the  pin-feathers,  others  later  and 
before  reaching  maturity.  The  hens  afterwards  pro- 
duced normal  chickens  with  another  cock.  Both 
strains  had  been  purely  bred  for  ten  or  more  years, 
and  none  of  the  fowls  had  been  blind  unless  from 
fights. 

"(This  case  was  reported  to  me  by  an  educated 
and  reliable  breeder  of  game-fowls.) 

"t.  A  hunting  mare  had  a  split  pastern  and  was 
then  used  for  breeding.  Her  first,  third,  and  fourth 
foals  were  sound,  the  second  one  had  '  almost  an  exact 
reproduction  of  the  mare's  unsoundness.' 

"(This  is  on  the  authority  of  the  celebrated  veteri- 
nary surgeon,  Clement  Stevenson,  as  occurring  under 
his  own  observation,  «  not  hearsay. '  Live  Stock  Jour- 
nal, London,  November  23,  1888,  p.  508.) 

"d.  A  female  (and  very  prolific)  cat,  when  about 
half  grown  met  with  an  accident.  '  Her  fine,  long  tail 
was  trodden  on  and  had  a  compound  fracture,  two  ver- 
tebrae being  so  displaced  that  they  ever  after  formed  a 
short  offset  between  the  near  and  far  end  of  the  tail, 
leaving  the  two  out  of  line.  At  first  I  noted  that  out 
of  every  litter  of  kittens  some  had  a  tail  with  a  querl 
in  it.'  With  successive  litters  the  deformity  increased, 
until  'not  a  kitten  of  the  old  cat  had  a  straight  tail, 
and  it  grew  worse  in  her  progeny  until  now  we  have 
not  a  cat  with  a  normal  tail  on  the  premises,'  (in  a  cat- 


HEREDITY.  433 

population  of  six  or  eight,  exclusive  of  young  kittens). 
'The  tails  are  now  in  part  mere  stumps,  some  have  a 
semicircular  sweep  sideways,  and  some  have  the  orig- 
inal querl.  Perhaps  the  deformity  was  somewhat 
aggravated  by  in-and-in  breeding  and  by  artificial  se- 
lection practised  by  my  Chinaman,  who,  with  the  per- 
versity of  his  race,  preferred  the  crooked  tails,  and 
thus  preserved  them  in  preference  to  the  normal  kit- 
tens. There  are  no  other  abnormally-tailed  cats  in 
the  neighborhood.' 

"This  is  the  essential  part  of  an  unpublished  letter 
from  that  keen  observer  and  eminent  scientist,  Prof. 
Eugene  W.  Hilgard  of  the  University  of  California. 

"  Numerous  cases  have  been  recorded  as  occurring 
with  mankind.  I  will  give  but  two,  both  of  which 
have  not  before  been  published. 

"  e.  A  person,  when  a  boy  of  ten  years,  cut  the 
terminal  phalange  of  the  little  finger  of  his  left  hand 
with  a  sickle.  The  joint  was  not  injured,  nor  was  the 
function  of  the  finger  seriously  impaired.  There  was, 
however,  an  obvious  deformity.  The  finger  was  ill- 
shaped  and  crooked,  and  the  nail  abnormal.  He  mar- 
ried and  had  two  children,  the  first  a  son,  with  normal 
fingers,  the  second  a  daughter,  who  had  the  little  fin- 
ger of  the  corresponding  (the  left)  hand  deformed 
from  birth  in  the  same  manner.  The  function  of  the 
finger  was  not  seriously  injured,  but  the  deformity  was 
precisely  the  same  in  shape,  even  to  the  malformation 
of  the  finger-nail.  She  died  at  thirty,  without  chil- 
dren, consequently  no  observation  on  a  succeeding 
generation  could  be  noted.  None  of  his  other  kindred 
had  malformed  fingers,  nor  had  any  ancestor  of  the 
child  for  at  least  three  generations,  and  there  was  no 
knowledge  of  any  such  in  the  more  remote  ancestry. 


434     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

"(This  case  was  related  to  me  in  full  detail  by  the 
father  with  the  deformed  finger,  and  with  whom  I  was 
personally  acquainted.  He  was  an  eminent  physician, 
the  president  of  a  large  and  reputable  medical  college, 
and  his  name  is  well  known  to  the  profession.) 

tlf.  A  woman  thirty- five  years  of  age  had  both 
kneepans  broken.  Erysipelas  and  other  complications 
prevented  the  use  of  the  usual  surgical  appliances  for 
keeping  the  severed  parts  together  while  healing,  so 
they  never  united  by  bony  union,  but  became  joined 
by  intervening  cartilage.  The  hurt  was  peculiarly 
painful  and  slow  of  healing,  because  of  the  complica- 
tions alluded  to,  but  the  general  health  was  fully  re- 
stored. For  some  years  after  healing  there  was  a  very 
pronounced  groove  or  furrow  along  the  line  of  fracture 
over  the  connecting  cartilage,  especially  in  the  right 
knee.  The  outer  edges  of  the  fractured  bone  were 
sharp  at  first,  but  ultimately  became  rounded  by  ab- 
sorption. Both  fractures  were  V-shaped.  The  right 
knee  had  the  parts  wider  separated  at  the  time  of  the 
accident,  and  was  again  partially  torn  asunder  three 
and  a  half  months  later,  and  the  furrow  consequently 
remained  very  much  broader  and  deeper  than  in  the 
other  knee.  About  four  months  (124  days)  after  the 
first  accident,  and  while  still  unable  to  walk,  she  gave 
birth  to  a  son.  No  abnormal  appearance  was  noticed 
at  the  time,  and  later  was  not  looked  for  until  the 
child  was  ten  or  more  years  old,  when  he  called  atten- 
tion to  the  matter  himself.  There  was  then  a  deep 
and  well-defined  groove  across  the  surface  of  the  right 
kneepan,  very  plainly  perceivable  through  the  skin. 
It  corresponded  precisely  in  shape  and  position  with 
the  fracture  and  the  later  furrow  in  the  corresponding 
bone  in  the  mother.  It  was  most  pronounced  before 


HEREDITY.  435 

the  age  of  sixteen.  After  that  the  edges  became  modi- 
fied by  growth  or  absorption,  becoming  less  sharp, 
following  in  this  respect  the  changes  that  gradually 
occurred  in  the  shape  of  the  bone  in  the  mother.  The 
son  is  otherwise  normal.  Three  other  children  of  the 
same  parents,  one  born  before  and  two  after  the  birth 
of  the  one  described,  are  entirely  normal.  The  ances- 
tors of  both  parents  are  known  for  several  generations 
(from  three  to  eight  in  the  several  lines)  and  all  were 
normal,  so  far  as  is  known." 

"(This  case  has  been  under  my  own  observation 
during  the  whole  period.) 

"It  will  be  noticed  that  in  the  cases  a,  b,  and/,  the 
injury  to  the  parent  occurred  shortly  before  or  during 
gestation,  and  that  the  healing  had  not  taken  place 
until  after  the  birth  of  the  offspring.  Also,  that  the 
function  of  the  organ  involved,  an  important  organ  in 
the  animal  economy,  was  at  the  time  suspended.  Also 
that  in  all  these  cases,  later  offspring  were  normal." 

e.   Inheritance  of  Characters  Due  to  Regional  Influences. 

Characters  of  this  kind  mostly  come  under  the  head 
of  Physiogenesis.  A  case  of  inheritance  is  thus  re- 
corded by  Brewer. 

"The  texture  and  certain  other  characters  of  wool 
which  are  of  practical  importance  to  manufacturers, 
depend  in  part  on  the  breed  and  health  of  the  animals, 
in  part  on  the  kind  of  food  and  on  its  uniformity  of 
supply,  and  in  part  on  local  conditions  of  climate, 
soil,  and  forage.  The  wool  grown  in  some  regions  is 
harsher  than  that  grown  in  others,  and  this  is  certainly 
an  acquired  character  in  that  it  takes  place  in  flocks 
taken  from  one  region  to  another.  I  have  specimens 
of  wool  alleged  to  have  been  taken  from  the  same 


436     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

flock,  the  same  individual  animals,  when  pastured  at 
two  stations.  The  first  were  shorn  when  the  sheep 
were  pastured  in  southeastern  Ohio,  where  the  sheep 
were  bred,  a  region  noted  for  certain  excellencies  of 
its  wool.  Taken  to  a  certain  portion  of  Texas,  and 
pastured  on  an  alkaline  soil,  the  wool  of  those  sheep 
took  another  character,  affecting  both  its  texture  and 
also  its  behavior  with  dyes.  Treated  in  the  same  vats, 
as  to  dye,  lac  and  mordant,  the  difference  is  very  ob- 
vious. 

"A  certain  harshness  of  the  wools  produced  in 
some  regions  where  the  soil  is  alkaline  or  salt,  the 
climate  dry,  and  the  forage  plants  characteristic  of 
such  regions,  is  widely  known  and  is  considered  a  de- 
fect by  manufacturers.  It  is  stated  that  when  a  flock 
is  taken  from  a  favorable  region  to  such  a  less  favor- 
able one  the  change  in  the  character  of  the  wool  begins 
immediately,  but  is  more  marked  in  the  succeeding 
fleeces  than  in  the  first.  It  is  also  alleged  that  the 
harshness  increases  with  succeeding  generations,  and 
that  the  flocks  which  have  inhabited  such  regions  sev- 
eral generations  produce  naturally  a  harsher  wool  than 
did  their  ancestors,  or  do  the  new-comers. 

"Now,  in  this  case,  the  deterioration  in  successive 
generations  cannot  possibly  be  due  to  panmixia,  the 
withdrawal  of  selection ;  on  the  contrary,  selection 
goes  on  under  the  new  conditions  just  as  carefully  as 
under  the  old,  and  often  more  so,  for  this  is  the  means 
used  to  lessen  the  evil. 

1 '  If  this  increase  in  the  harshness  of  the  wool  of 
succeeding  generations  is  due  in  part  to  the  inheri- 
tance of  an  acquired  character,  it  is  very  understand- 
able. That  it  is  a  congenital  adventitious  variation 


HEREDITY.  437 

coincident  in  all  the  individuals  of  immense  flocks,  is 
a  mathematical  absurdity. 

"We  have  an  analogous  regional  character  in  the 
hoofs  of  horses.  From  early  times  it  has  been  a  known 
fact  that  the  feet  of  horses  produced  in  mountainous 
and  hilly  regions  stand  travel  on  hard  roads  and  on  city 
pavements  better  than  those  bred  on  softer  low  lands, 
however  rich  and  fertile  the  latter  may  be.  European 
writers  of  previous  centuries  are  very  specific  on  this 
point.  Jacquet,  over  two  centuries  ago,  cites  it  as  a 
fact  true  alike  in  Spain,  Italy,  and  other  countries  of 
Europe.  I  have  interviewed  the  livery-stable  men  in 
various  eastern  cities  as  to  the  relative  character  in 
that  particular  of  the  horses  bred  in  the  hilly  regions 
of  New  England,  New  York,  and  Pennsylvania,  com- 
pared with  those  produced  on  the  prairies,  and  the 
testimony  is  almost  unanimous  to  the  same  effect. 
The  old  Vermont  bred  horses  are  still  famous. 

"This  regional  character  cannot  be  a  matter  of  se- 
lection and  adventitious  variation.  It  must  be  related 
to  the  environment  alone,  and  environment  can  only 
act  on  the  living  individual.  If  this  fact  is  due  to  the 
inheritance  of  acquired  characters,  it  is  very  easily 
understood.  The  different  effects  of  exercise  of  the 
feet  of  the  growing  animal  in  the  one  case  on  the  hard, 
stony  soil  of  the  hills,  in  the  other,  on  the  softer  and 
fine  soil  of  the  prairies,  makes  a  difference  in  the  ac- 
quired characters,  a  difference  of  the  very  kind  spoken 
of,  and  which  becomes  congenital." 

At  the  close  of  this  series  of  papers  Brewer  re- 
marks :  "The  art  of  breeding  has  become  in  a  meas- 
ure an  applied  science ;  the  enormous  economic  inter- 
ests involved  stimulate  observation  and  study,  and 
what  is  the  practical  result?  This  ten  years  of  active 


438    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

promulgation  of  the  new  theory  has  not  resulted  in  the 
conversion  of  a  single  known  breeder  to  the  extent  of 
inducing  him  to  conform  his  methods  and  practice  to 
the  theory.  My  conclusion  is  that  they  are  essentially 
right  in  their  deductions  founded  on  their  experience 
and  observations,  namely,  that  acquired  characters 
may  be,  and  sometimes  are,  transmitted,  and  that  the 
speculations  of  the  Weismann  school  of  naturalists  are 
unfounded." 

5    THE  CONDITIONS  OF  INHERITANCE. 

Since  the  evidence  adduced  must  be  regarded  as 
proving  that  characters  acquired  by  an  organism  may 
be  transmitted  by  inheritance,  we  next  endeavor  to 
ascertain  what  information  is  within  our  reach  which 
can  throw  light  on  this  mysterious  process.  Although 
Weismann  has  demonstrated  the  isolation  and  stability 
of  the  germ-plasma  to  exceed  that  of  other  tissues,  he 
has  not  proven  that  it  is  entirely  inaccessible  to  exter- 
nal influences.  He  admits  that  its  continual  subdivi- 
sion by  the  development  from  it  of  the  embryonic 
soma,  would  have  speedily  reduced  it  to  an  infinitesi- 
mal quantity,  were  it  not  that  it  grows  by  accession  of 
nutritive  material  like  other  tissues,  which  nutritive 
material  is  furnished  by  the  soma.  The  accessibility 
of  the  germ-plasma  to  stimuli  which  affect  the  soma  is 
then  clearly  possible. 

The  effect  of  the  specialization  of  tissues  on  their 
nutrition  and  repair  after  injury,  is  well  known.  Nu- 
trition of  each  tissue  produces  only  that  tissue.  Re- 
pair or  restoration  of  parts  is  confined  to  the  repro- 
duction of  a  tissue  similar  to  the  part  lost,  or  similar 
to  some  unfinished  or  embryonic  stage  of  it.  The 
lower  we  descend  in  the  scale  of  life,  the  more  com- 


HEREDITY.  439 

plete  is  the  reproduction  of  a  lost  part.  The  special- 
ization of  the  higher  organisms  deprives  the  tissue  of 
the  capacity  for  exact  reproduction.  As  an  example 
of  the  reduction  of  this  capacity,  I  cite  the  reproduc- 
tion of  the  tail  of  lizards,  where  no  vertebrae  are  repro- 
duced, but  in  its  place  a  notochord  ;  while  the  squa- 
mation  presents  a  simpler  character  than  that  of  the 
normal  tail.  The  possibility  of  reproducing  the  entire 
organism  is  restricted,  in  the  multicellular  animals,  to 
the  germ-plasma,  which  therefore  may  be  regarded  as 
retaining  the  characteristic  of  the  protozoon,  which 
reproduces  itself  by  division.  But  in  the  multicellular 
plants  the  power  of  reproduction  of  the  entire  organ- 
ism from  any  of  its  parts,  is  retained  to  a  much  greater 
degree  than  in  multicellular  animals.  The  reproduc- 
tion of  plants  by  cuttings,  buds,  tubers,  and  even  by 
single  leaves,  is  well  known  ;  a  characteristic  which  is 
due  to  the  general  distribution  of  unspecialized  proto- 
plasm throughout  the  organism.  Inheritance  of  char- 
acters is  in  these  cases  known  to  be  very  exact,  and 
there  can  be  here  no  isolation  of  the  germ-plasma.  This 
isolation  is  progressively  more  pronounced  as  we  rise 
in  the  scale  of  specialization  of  structure,  but  that  it 
ever  becomes  absolute,  the  facts  before  us  forbid  us  to 
believe. 

Having  thus  seen  that  the  plasma  of  the  germ-cells 
is  open  to  the  influence  of  stimuli,  let  us  see  how  it  is 
possible  that  such  stimuli  can  be  transmitted  to  it,  and 
how  they  could  affect  growth  of  the  embryo. 

It  has  been  shown  that  impressions  experienced  by 
an  animal  during  one  stage  of  development  may  be 
effective  in  causing  the  appearance  of  new  structure  in 
a  later  stage.  I  have  already  quoted  (Chap.  V.)  from 
Poulton  the  results  of  experiments  on  the  colors  of 


440    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION 

Lepidoptera  "by  several  English  entomologists.  By 
exposure  to  different  colors,  of  larvae  which  were  ap- 
proaching the  period  of  pupation,  corresponding  colors 
were  produced  in  the  pupae.  Thus  black,  dark,  green, 
and  yellow  larvae,  and  larvae  with  gilt  spots  or  entirely 
gilded,  were  produced  at  will.  In  this  instance  the 
dynamic  effect  produced  by  the  exposure  was  stored 
for  the  period  which  elapsed  between  the  exposure  of 
the  larva  and  the  full  development  of  the  pupa.  In 
another  experiment,  larvae  which  were  in  the  act  of 
weaving  cocoons,  on  exposure  to  certain  colors,  were 
induced  to  weave  cocoons  of  corresponding  color. 
This  experiment  demonstrates  that  a  stimulus  may  be 
transmitted  to  a  gland  so  as  to  modify  the  character 
of  its  secretion  in  a  new  direction.  From  both  experi- 
ments we  learn  the  transmissibility  of  energy  from  the 
point  of  stimulus  to  a  remote  region  of  the  body,  and 
its  conversion  into  growth  energy  (in  this  case  by 
Physiogenesis).  This  prepares  us  to  look  upon  hered- 
ity as  an  allied  phenomenon,  i.  e.,  the  transmission  of 
a  special  energy  from  a  point  of  stimulus  to  the  germ- 
cells,  and  its  composition  there  with  the  emphytogenic 
(inherited)  energy  into  bathmism  (or  evolutionary  en- 
ergy). 

The  relation  of  inherited  and  acquired  characters 
in  a  series  of  generations  may  be  graphically  repre- 
sented as  follows :  Let  S  represent  the  aggregate  of 
character  of  the  body  (soma)  of  a  given  species  in  pro- 
cess of  progressive  evolution  or  acceleration.  Let  g 
represent  the  aggregate  of  characters  potential  (or  dy- 
namically present)  in  the  germ  cells  of  the  same  indi- 
vidual. For  the  sake  of  simplification  of  the  problem 
I  consider  here  only  one  sex,  and  imagine  the  repro- 
duction to  be  parthenogenetic.  Let  A  represent  the 


HEREDITY. 


441 


new  character  acquired  by  the  soma  under  the  appro- 
priate stimulus,  and  let  a  represent  the  same  charac- 
teristic as  it  is  impressed  on  the  germ-plasma  of  the 
same  individual  at  the  same  time,  and  in  consequence 
of  the  same  stimulus.  The  history  of  the  acquisition 
and  incorporation  of  newly  acquired  characters  by  the 
line  of  descent  originating  with  the  species  S-\-g,  may 
be  represented  as  follows,  for  successive  generations, 
which  are  numbered  i,  2,  3,  etc. 


/  SA 


Fig.  120. — Diagram  explanatory  of  Diplogenesis. 

Under  the  appropriate  stimulus  the  soma  S  acquires 
A,  and  the  germ  plasma  g  the  identical  a1  as  the  first 
stage.  The  character  A  a1  being  only  inheritable  via 
the  germ-plasma,  it  is  represented  by  a1  in  the  second 
stage  or  generation,  where  it  appears  as  an  addition 
to  the  characters  of  S  and  g,  so  that  the  soma  of  the 
second  generation  is  represented  by  the  expression 
Sal,  and  the  germ-plasma  by  g(al)  ;  (on  the  supposi- 


442    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

tion  that  SA  -f-  gal  represents  the  first  of  a  line  in  which 
a  given  character  appears).  A  new  character  or  an 
additional  increment  of  the  same  character,  appears 
in  the  second  stage  of  acceleration  "2,"  and  is  repre- 
sented as  before,  by  Aa2,  the  A  appearing  in  the  soma, 
and  the  a2  being  added  to  the  character  of  the  germ- 
plasma.  In  the  third  stage,  the  new  character  a2  ap- 
pears in  the  soma,  which  now  becomes  Sala?.  The  a2 
acquired  by  the  germ-plasma  of  the  second  stage,  is 
inherited  by  that  of  the  third,  which  is  therefore  rep- 
resented by  g(ala2~).  To  the  third  stage  is  now  added 
the  acquisition  Aa3.  The  cP  is  again  incorporated  into 
the  soma  of  the  succeeding  or  fourth  stage,  which  is 
therefore  represented  by  the  expression  S0W;  while 
the  germ-plasma  of  the  same  (fourth,  "4,")  stage,  is 
represented  by  g(ala*cP) ,  and  so  on.  The  lines  of  im- 
mediate inheritance  are  represented  by  straight  lines. 
The  vertical  lines  represent  the  descent  of  characters 
from  one  type  of  the  germ-plasma  to  a  succeeding 
one  ;  and  the  oblique  lines  represent  the  transmission 
of  the  same  characters  to  the  soma  into  which  it  grows, 
as  the  succeeding  generation  or  stage. 

The  letters  a1,  a2,  etc.,  expressive  of  characters  ac- 
quired by  the  germ-plasma,  are  numbered  for  identifi- 
cation only.  Should  the  influences  derived  from  the 
ancestry  of  the  other  sex  be  added  to  the  diagram  its 
complexity  would  become  inconvenient,  and  they  are 
therefore  omitted.  It  is  to  be  also  observed,  that  the 
enumeration  of  generations  as  immediately  successive, 
as  1—2-3  etc.,  is  to  be  understood  as  indicating  succes- 
sion only,  and  not  any  exact  number  of  generations. 

In  the  hypothesis  of  heredity  above  outlined,  it  is 
insisted  that  the  effects  of  use  and  disuse  are  two-fold ; 
viz. :  the  effect  on  the  soma,  and  the  effect  on  the 


'HEREDITY.  443 

germ-plasma.  Those  who  sustain  the  view  that  ac- 
quired characters  are  inherited,  must,  I  believe,  un- 
derstand it  as  thus  stated.  The  character  must  be 
potentially  acquired  by  the  germ-plasma  as  well  as  ac- 
tually by  the  soma.  Those  who  insist  that  acquired 
characters  are  not  inherited,  forget  that  the  character 
acquired  by  the  soma  is  identical  with  that  acquired 
by  the  germ-plasma,  so  that  the  character  acquired  by 
the  former  is  inherited,  but  not  directly.  It  is  acquired 
contemporaneously  by  the  germ-plasma,  and  inherited 
from  it.  There  is  then  truth  in  the  two  apparently  op- 
posed positions,  and  they  appear  to  me  to  be  harmon- 
ized by  the  doctrine  above  laid  down,  which  I  have 
called  the  Theory  of  Diplogenesis,  in  allusion  to  the 
double  destination  of  the  effects  of  use  and  disuse  in 
inheritance. 

From  the  preceding  considerations  we  learn  that  a 
new  character  is  not  inherited  unless  it  is  acquired  by 
germ-plasma,  as  well  as  by  the  soma.  Should  it  fail 
of  the  former  it  will  not  be  inherited,  although  it  may 
appear  in  the  soma.  It  is  also  evident  that  the  same 
character  appears  in  the  soma  of  later  generations  by 
virtue  of  its  inheritance  by  their  germ-plasma.  Hence 
should  it  fail  to  appear  in  the  adult  soma  of  one  gen- 
eration, it  might  arise  in  a  later  one ;  and  hence  the 
possibility  of  atavism,  and  an  alternation  of  genera- 
tions. Intermittent  stimulus  might  be  followed  by  in- 
termittent activity  of  growth  energy.  This  would  be 
especially  apt  to  occur  during  the  assumption  of  sex- 
uality by  animals  and  plants  whose  reproduction  had 
been  performed  by  cell-division  or  budding  only.  And 
such  is  the  character  of  most  types  of  alternate  gene- 
rations ;  a  sexual  type  alternates  with  a  non-sexual 
type.  The  advantages  being  on  the  side  of  sexual  re- 


444    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


production  on  account  of  its  increased  opportunity  of 
variation,  it  has  replaced  the  more  primitive  method 
by  the  process  of  natural  selection. 

The  time  when  the  impressions  of  physical  habits 
are  conveyed  to  the  reproductive  elements  has  an  im- 
portant bearing  on  the  question  of  inheritance.  Pro- 
fessor Osborn l  has  thus  classified  the  agencies  which 
lie  at  the  basis  of  organic  evolution.  Opposite  to  each 
he  states  the  theories  which  have  been  proposed  to 
account  for  them  : 

A.    Onto  genie  Variations. 

a.    Gonagenic,  i.  e.,  those  aris-  Theoretically  connected  with 

ing  in  the  germ-cells,  including       pathological,  nutritive  chemico 

physical,  nervous  influences,  in- 
cluding the  doubtful  phenomena 
of  Xenia  and  Telegony. 

Theoretically  connected  with 
influences  named  above,  also 
with  the  combination  of  diverse 
ancestral  characters,  Amphi- 
mixis of  Weismann. 


"blastogenic  "  in  part  of  Weis- 
mann, the  "  primary  variations" 
of  Emery. 

b.  Gamogenic,  i.  e.,  those  aris- 
ing from  maturation  and  fertili- 
zation,   including  the    "blasto- 
genic" in   part   of   Weismann, 
and  secondary  or  Weismannian 
variations  of  Emery. 

c.  Embryogenic,  i.e.,  those  oc- 
curring  during   early  cell-divi- 
sion,  including  the  blastogenic 
and  somatogenic  of  Weismann. 


d.  Somatogenic,  i.e.,  those  oc- 
curring during  larval  and  later 
development  after  the  formation 
of  the  germ-cells. 

B.  Phylogenic  Variations. 

Variations  from  types  originating  in  any  of  the  above  stages 
which  become  hereditary. 


Theoretically  connected  with 
extensive  anomalies  due  to  ab- 
normal segmentation,  and  other 
causes  observed  in  the  mechan- 
ical embryology  of  Roux,  Wil- 
son, Driesch,  and  others. 

Connected  with  reactions  be- 
tween the  hereditary  develop- 
ment forces  of  the  individual 
and  the  environment. 


1  American  Naturalist,  1895,  p.  426:  "On  the   Hereditary  Mechanism  and 
the  Search  for  Unknown  Factors  of  Evolution  " 


HEREDITY.  445 

Osborn  points  out  that  Buffon  appealed  to  the 
"direct  action  of  the  environment"  as  a  cause  of  evo- 
lution, in  so  general  a  way,  as  to  embrace  all  the  con- 
ditions above  enumerated.  St.  Hilaire  dwelt  on  the 
embryogenic  influences,  while  Lamarck  laid  stress  on 
the  somatogenic.  Darwin  only  discussed  variation 
after  it  came  into  being. 

The  distinctions  pointed  out  by  Osborn  relate  to 
the  period  of  life  at  which  modifying  influences  are 
experienced  ;  that  is,  they  are  time  distinctions.  They 
must  all,  however,  be  included  under  two  heads  when 
the  sources  of  influence  are  considered.  That  is,  they 
must  proceed  from  the  organism  itself,  or  from  the  en- 
vironment directly.  Those  proceeding  from  the  or- 
ganism may  also  be  divided  into  two  classes,  viz., 
those  which  are  inherent  in  the  physical  and  chemical 
characters  of  protoplasm,  and  those  which  have  been 
acquired  by  generations  prior  to  any  given  one  under 
consideration.  In  this  work  I  attend  first  to  the  prob- 
ably efficient  or  phylogenetic  causes,  and  these  may  be 
regarded  as  having  been  at  some  time  or  another  dur- 
ing the  history  of  the  phylum  as  somatogenic.  On 
this  view,  I  have  regarded  the  life  of  an  animal  as 
divided  into  three  periods  ;  those  of  embryonic  life,  of 
adolescence,  and  of  maturity.  During  embryonic  life 
impressions  are  exclusively  somatic,  and  can  be  only 
obtained  through  or  from  parental  stimulus  and  parental 
environment.  Such  will  reach  the  embryo  through  nu- 
trition, and  through  the  direct  mechanical  contacts  and 
strains  of  the  environment.  The  environment  of  unpro- 
tected embryos  is  external  to  the  parent ;  that  of  long 
protected  embryos  is  the  walls  of  the  oviduct,  uterus, 
etc.,  within  the  parent.  Ryder  has  alleged  with  much 
reason  that  the  nature  of  the  contact  of  the  chorion  with 


446    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

the  walls  of  the  oviducts  or  uterus  has  determined  the 
shape  of  the  placenta  ;  and  that  the  invagination  of  the 
embryo  which  resulted  in  the  development  of  the  am- 
nion  is  a  result  of  gravitation.  While  these  facts  have 
an  important  bearing  on  the  study  of  inheritance,  they 
have  but  a  collateral  relation  to  evolution  ;  since  the 
embryo,  whether  in  utero  or  in  ovo,  has  little  oppor- 
tunity of  experiencing  the  external  influences  which  are 
only  possible  at  later  periods  of  life.  It  is  during  ado- 
lescence that  the  normal  activities  of  maturity,  except 
reproduction,  are  first  practised,  whether  inherited  or 
learned  for  the  first  time.  The  superior  capacity  of  the 
adolescent  stage  for  acquisition  in  all  directions  is  well 
known,  and  it  is  reasonable  to  suppose  that  since  growth 
is  not  completed,  changes  in  its  details  can  be  most 
readily  introduced.  It  is  to  this  period  of  life  then  that 
we  must  look  for  the  effective  influence  of  the  factors 
of  evolution  in  the  acquisition  of  new  characters  of  the 
soma.  And  if  the  nervous,  muscular  and  other  tissues 
react  at  this  period  most  readily  to  external  stimuli, 
it  is  to  be  supposed  that  the  developing  reproductive 
cells  possess  the  same  characteristic,  and  record  in 
their  molecular  movements  the  influences  which  are 
experienced  by  the  entire  body.  Such  influences  on 
the  reproductive  cells,  repeated  millions  of  times  from 
generation  to  generation,  must  produce  a  definite  effect 
on  them,  in  spite  of  the  conservatism  which  their  com- 
parative isolation  imposes  on  them.1 

The  transmission  of  acquired  characters  is  evi- 
dently accomplished  during  the  adult  period.  While 
the  influence  on  the  soma  is  greatest  during  ado- 
lescence, the  influence  on  the  germ- plasma  is  prob- 
ably important  during  maturity,  because  habits  formed 

\Anterican  Naturalist,  December,  1889,  "On  Inheritance  in  Evolution." 


HEREDITY.  447 

during  adolescence  are  now  practised  with  especial 
energy  and  frequency.  The  influence  on  the  constantly 
renewed  germ-plasma  is  correspondingly  greater,  and 
transmission  is  of  course  more  certain.  Some  charac- 
ters seem  to  have  been  mainly  acquired  during  matur- 
ity. Such  is  the  permanent  dentition  of  the  higher 
Mammalia,  which  does  not  appear  until  or  after  ma- 
turity. In  this  case  the  influence  of  use  on  the  germ- 
plasma  must  be  more  energetic  than  that  on  the  soma. 
It  is,  however,  not  unlikely  that  the  fundamental  char- 
acters of  mammalian  dentition  were  laid  during  ado- 
lescence by  direct  influence  on  the  temporary  dentition. 
The  tritubercular  molar  was  established  at  that  time 
and  owes  its  present  existence  to  inheritance.  Only 
the  sectorial  and  lophodont  types  have  been  added 
since  the  extensive  development  of  the  milk  dentition 
in  geologic  time. 

The  chief  source  from  which  acquired  characters 
are  introduced  into  the  germ-plasma,  and  hence  into 
the  soma  of  the  next  generation,  is  probably  the  sper- 
matozooid,  since  it  is  endowed  with  a  greater  kinetic 
energy  than  the  ovum.  The  latter  furnishes  nutritive 
material  for  the  supply  of  the  needs  of  growth.  That 
the  male  is  the  chief  source  of  variation  is  also  indi- 
cated in  the  numerous  cases  when  he  is  more  active 
than  the  female,  and  hence  more  capable  of  supplying 
the  stimulus  of  use. 

The  manner  in  which  influences  which  have  af- 
fected the  general  structure  are  introduced  into  the 
germ-cells  remains  the  most  difficult  problem  of  biol- 
ogy. For  its  explanation  we  have  nothing  as  yet  but 
hypotheses.  The  one  which  has  seemed  to  me  to  be 
the  most  reasonable  belongs  to  the  field  of  molecular 
physics,  and  it  must  be  long  before  it  is  either  proved 


448    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

or  disproved.  I  have  termed  it  a  "dynamic  theory," 
and  it  is  in  some  respects  similar  to  that  subsequently 
proposed  by  Haeckel  under  the  name  of  the  "peri- 
genesis  of  the  plastidule. "  I  have  already  referred  to 
the  phenomena  of  the  building  or  growth  of  the  added 
characters  which  constitute  progressive  evolution  as 
evidence  of  the  existence  of  a  peculiar  species  of  en- 
ergy, which  I  termed  bathmism.  This  is  to  be  ex- 
plained as  a  mode  of  motion  of  the  molecules  of  living 
protoplasm,  by  which  the  latter  build  tissue  at  par- 
ticular points,  and  do  not  do  so  at  other  points.  This 
action  is  most  easily  observed  in  the  beginnings  of 
growth,  as  in  the  segmentation  of  the  oosperm,  the 
formation  of  the  blastodermic  layers,  of  the  gastrula, 
of  the  primitive  groove,  etc.  In  the  meroblastic  em- 
bryo the  energy  is  evidently  in  excess  at  one  part  of 
the  oosperm,  and  in  defect  at  another.  This  is  a  sim- 
ple example  of  the  "location  of  growth  force  or  bath- 
mism." In  all  folding  or  invagination  there  is  ex- 
cess of  growth  at  the  region  which  becomes  the  con- 
vex face  of  the  fold;  i.  e.,  a  location  or  especial  ac- 
tivity of  bathmism  at  that  point.  All  modifications  of 
form  can  be  thus  traced  to  activity  of  this  energy  at 
particular  points.  A  basis  is  thus  laid  for  a  more  or 
less  complex  organism,  and  the  channels  of  nutritive 
pabulum  being  once  established,  the  location  or  dis- 
tribution of  the  energy  is  assured  in  the  directions  in 
which  they  lead.  Thus  with  the  establishment  of  cir- 
culating channels  nutrition  is  definitely  guided  to  par- 
ticular points.  It  is  evident  that  on  this  hypothesis 
the  bases  of  evolutionary  change  are  laid  in  the  em- 
bryonic tissues,  where  bathmism  displays  its  activity 
in  producing  the  base  forms  on  which  all  subsequent 
structure  is  moulded. 


HEREDITY.  449 

/ 

The  building  energy  being  thus  understood  to  be  a 
mode  of  molecular  motion,  we  are  not  at  liberty  to 
suppose  that  its  existence  is  dependent  on  the  dimen- 
sions of  the  organic  body  which  exhibits  it.  It  is  as  char- 
acteristic of  the  organic  unit  or  plastidule  as  the  mode 
of  motion  which  builds  the  crystal  is  of  the  simplest 
molecular  aggregate  from  which  the  crystal  arises. 
Bathmism  has,  however,  no  other  resemblance  to 
crystalloid  cohesion.  The  latter  is  a  simple  energy 
which  acts  within  geometrically  related  spaces,  with- 
out regard  to  anything  else  but  the  present  compulsion 
of  superior  weight-energy.  In  bathmism  we  see  the 
resultant  of  innumerable  antecedent  influences,  which 
builds  an  organism  constructed  for  adaptations  to  the 
varied  and  irregularly  occurring  contingencies  which 
characterize  the  life  of  living  beings.  As  this  resultant 
is  distinctive  for  every  species,  bathmism  must  be 
regarded  as  a  generic  term,  and  the  characteristic 
growth-energy  of  each  species  as  distinct  species  of 
energy,  which  presents  also  diversities  expressive  of 
the  peculiarities  of  individuals. 

The  preceding  statements  do  not,  of  course,  con- 
stitute an  explanation  of  the  exact  manner  in  which  a 
stimulus  which  effects  say  the  contraction  of  a  muscle, 
effects  molecular  movements  of  the  nuclei  of  the  re- 
productive cells.  This  is  a  question  of  organic  molec- 
ular physics,  a  science  which  has  made  scarcely  a  be- 
ginning. That  the  transmission  of  such  influence  is 
through  nutritive  channels,  by  the  intermediation  of  a 
nervous  structure  where  one  exists,  may  be  supposed. 
Poulton's  experiments  on  Lepidoptera,  already  cited, 
led  him  to  believe  that  the  effect  of  color-environment 
was  transmitted  to  the  pigment-cells  through  the  me- 
dium of  the  nervous  system.  That  the  modus  operandi 


450    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

is  similar  to  that  which  produces  reflexes  may  be  also 
reasonably  supposed.  How  the  record  of  these  move- 
ments become  reflexes,  is  concentrated  in  a  reproduc- 
tive cell,  is  a  question  to  be  solved  only  in  a  more  ad- 
vanced stage  of  knowledge  of  organic  physics  than  we 
now  possess. 

Speculation  in  this  direction  takes  the  following 
forms.  According  to  one  view  the  energy  or  molecu- 
lar movement  must  be  transmitted  to  the  germ-plasma 
through  a  material  or  molecular  basis.  This  basis,  it 
may  be  supposed,  must  be  that  which  receives  the 
mechanical  impression  which  is  to  produce  a  corre- 
sponding modification  of  growth-energy  in  the  ovum 
or  spermatozooid ;  that  is,  in  the  case  of  a  modified 
bone-articulation,  particles  of  matter  must  pass  from 
the  latter  through  the  medium  of  the  circulation  to 
the  reproductive  cells.  The  alternative  hypothesis  is, 
that  the  energy  which  causes  the  active  region  to  make 
or  omit  to  make  a  given  movement,  the  result  of  which 
is  to  be  structural  modification  in  the  young,  is  im- 
pressed through  protoplasmic  channels  on  the  germ- 
cells  of  either  sex.  In  this  case  the  transmission  of 
particles  of  matter  is  not  necessary,  as  material  connec- 
tion through  the  cells,  nervous  or  other,  already  exists. 

To  the  first  of  these  points  of  view  belong  the  pan- 
genesis  theory  of  Darwin,  and  the  modified  pangenesis 
of  Weismann.  These  hypotheses  present  the  difficulty 
that  we  must  conceive  of  each  particle  or  "gemmule" 
derived  from  a  given  part  of  the  organism  finding  its 
way  through  the  circulation  to  its  exact  place  in  the 
growing  embryo  ;  or  otherwise,  of  transmitting  its  pe- 
culiar mode  of  motion  to  the  correct  molecules  of  the 
embryo,  without  error  as  to  locality.  The  difficulties 
to  be  encountered  in  accomplishing  such  a  feat  seem 


HEREDITY.  451 

to  be  insuperable.  Hyatt  well  expresses  these  in  the 
following  language :  ' '  Every  purely  corpuscular  throng 
.  .  .  must  not  only  account  for  a  difficulty  as  great  as 
that  of  the  camel  and  the  needle's  eye,  but  must  also 
account  for  putting  the  numberless  characters  derived 
from  the  entire  caravan  of  its  immediate  progenitors 
and  remote  wild  ancestors  and  their  progenitors  back 
to  the  origin  of  their  phylum,  through  the  same  nar- 
row tunnel.  This  physical  difficulty  is  still  further 
enhanced  by  the  fact  that  the  ova  and  spermatozoa  do 
not  increase  in  size  in  proportion  to  the  increasing 
number  of  characters  transmitted."  (Proc.  Boston  Soc. 
N.  H.,  1893,  p.  70.) 

The  transmission  of  a  mode  of  motion  organized  in 
a  central  nervous  system,  is  less  inconceivable.  This 
central  system  is  the  seat  of  a  composition  of  incoming 
stimuli  and  of  outgoing  energies,  the  resultant  of  both 
combined  constituting  the  active  agency  in  the  pro- 
duction of  automatic  adaptive  or  intelligent  adaptive 
movements  of  any  and  all  of  the  organs.  It  appears 
to  me  that  we  can  more  readily  conceive  of  the  trans- 
mission of  a  resultant  form  of  energy  of  this  kind  to 
the  germ-plasma  than  of  material  particles  or  gem- 
mules.  Such  a  theory  is  sustained  by  the  known  cases 
of  the  influence  of  maternal  impressions  on  the  grow- 
ing foetus.  Going  into  greater  detail,  we  may  compare 
the  building  of  the  embryo  to  the  unfolding  of  a  record 
or  memory,  which  is  stored  in  the  central  nervous  or- 
ganism of  the  parent,  and  impressed  in  greater  or  less 
part  on  the  germ-plasma  during  its  construction,  in  the 
order  in  which  it  was  stored.  This  record  may  be 
supposed  to  be  woven  into  the  texture  of  every  organic 
cell,  and  to  be  destroyed  by  specialization  in  modified 
cells  in  proportion  as  they  are  incapable  of  repro- 


452    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

ducing  anything  but  themselves.  The  basis  of  mem- 
ory is  reasonably  supposed  to  be  a  molecular  (or 
atomic)  arrangement  from  which  can  issue  only  a 
definite  corresponding  mode  of  motion.  That  such 
an  arrangement  exists  in  the  central  nervous  organism 
is  demonstrated  by  automatic  and  reflex  movements. 
It  is  also  demonstrated  by  the  fact  that  the  memory 
of  the  position  and  parts  of  amputated  limbs  is  re- 
tained by  the  sensory  center,  so  that  irritation  of  the 
stump  is  referred  to  the  lost  limb.  That  the  entire 
record  is  not  repeated  in  automatic  and  reflex  acts, 
but  only  that  part  of  it  which  was  last  acquired,  may 
be  regarded  as  due  to  the  muscular  and  other  systems 
concerned  in  it  having  performed  it  most  recently,  and 
having  for  a  longer  or  shorter  period  omitted  to  per- 
form the  older  movement,  because  the  latest  struc- 
tures of  the  organs  would  render  the  performance  of 
the  old  movements  impossible.  In  other  words,  the 
physiological  division  of  labor  extends  to  memory  at 
the  basis.  In  the  case  of  the  germ-plasma  no  other 
specialization  exists,  so  that  the  entire  record  may  be 
repeated  stage  after  stage,  thus  producing  the  succes- 
sion of  type-structures  which  embryology  has  made 
familiar  to  us.  In  the  process  of  embryonic  growth, 
one  mode  of  motion  would  generate  its  successor  in 
obedience  to  the  molecular  structural  record  first  laid 
down  in  the  ovum  and  spermatozooi'd,  and  then  com- 
bined and  recomposed  on  the  union,  of  the  two  in  the 
oospore,  or  fertilized  ovum. 

If  the  doctrine  of  kinetogenesis  be  true,  this  energy 
has  been  moulded  by  the  interaction  of  the  living  be- 
ing and  its  environment.  It  is  the  recorded  expression 
of  the  habitual  movements  of  the  organism  which  have 
become  impressed  on,  and  recorded  in,  the  reproduc- 


HEREDITY.  453 

tive  elements.  It  is  evident  that  these  and  the  other  or- 
ganic units  of  which  the  organism  is  composed  possess 
a  memory-structure  which  determines  their  destiny  in 
the  building  of  the  embryo.  This  is  indicated  by  the  re- 
capitulation of  the  phylogenetic  history  of  its  ancestors 
displayed  in  embryonic  growth.  This  memory  has 
perhaps  the  same  molecular  basis  as  the  conscious 
memory,  but  for  reasons  unknown  to  us,  consciousness 
does  not  preside  over  its  activities.  The  energy  which 
follows  its  guidance  has  become  automatic,  and  it 
builds  what  it  builds  with  the  same  regardlessness  of 
immediate  surroundings  as  that  which  is  displayed  by 
the  crystalline  growth-energy.  It  is  incapable  of  a 
new  design,  except  as  an  addition  to  its  record. 

Were  all  cells  identical  in  characters,  every  one 
would  retain  the  structural  record,  or  memory  of  its 
past  physical  history,  as  do  the  unicellular  organisms. 
Evolution  has,  however,  so  modified  most  of  the  struc- 
tural units  of  the  organic  body  that  none  but  the  ner- 
vous and  reproductive  cells  retain  this  record,  in 
greater  or  less  perfection.  The  nervous  cells  have 
been  specialized  as  the  recipients  of  new  impressions, 
and  the  excitors  of  definite  corresponding  movements 
in  the  cells  of  the  remainder  of  the  organism.  The 
somatic  cells  retain  only  the  record  or  memory  of  their 
special  function.  On  the  other  hand,  the  reproduc- 
tive cells,  which  most  nearly  resemble  the  independent 
unicellular  organisms,  retain  first  the  impressions  re- 
ceived during  their  primitive  unicellular  ancestral  con- 
dition; and  second,  those  which  they  have  acquired 
through  the  organism  of  which  they  have  been  and  are 
only  a  part.  The  medium  through  which  they  can 
receive  such  impression  is  continuous  protoplasm. 
Whether,  in  the  higher  animals,  it  is  effected  through 


454    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

that  system  of  cells  called  the  nervous  system,  which 
has  been  specialized  through  use  and  natural  selection 
to  receive  impressions  from  without,  and  to  transmit 
them  to  such  parts  of  the  organism  as,  are  capable  of 
receiving  them,  or  whether  it  is  transmitted  through 
other  media,  as  in  lower  animals  and  in  plants  which 
possess  no  such  system,  is  unknown.  The  only  cells 
which  can  retain  the  entire  record  in  the  higher  ani- 
mals are  the  reproductive  cells.  In  the  lower  animals 
and  plants  it  is  well  known  that  germ-plasma  is  not 
confined  to  reproductive  organs,  but  is  widely  dissemi- 
nated throughout  the  organism.  In  some  forms  it 
seems  that  all  of  the  sarcode  is  capable  of  reproduction. 

This  is  the  logical  result  of  the  considerations 
which  have  occupied  the  preceding  pages,  and  is  the 
carrying  out  of  the  bathmism  theory  of  heredity,  of 
which  I  have  given  hitherto  only  the  bare  outline. 

Since  Darwin,  successive  contributions  have  been 
made  to  the  theory  of  heredity  in  its  relation  to  evolu- 
tion. In  1868  and  1871  the  present  writer  advanced 
the  dynamic  hypothesis,  but  made  no  attempt  to  ex- 
plain the  mode  of  conveyance  of  dynamic  impressions 
and  modifications  to  the  germ-cells.  The  theory  of 
"perigenesis,"  proposed  by  Haeckel  in  1873,  is  of  the 
same  character,  and  is  deficient  in  the  same  way.  The 
modified  pangenesis  theory  of  Brooks,  published  in 
I883,1  attempts  to  supply  the  defect  found  in  the  pre- 
vious conceptions,  but  does  so  by  assuming  with  Dar- 
win the  intermediation  of  gemmules,  a  hypothesis  to 
which  sufficient  objection  has  been  made  by  Galton 
and  others.  Brooks's  theory  also  fails  to  admit  the 
origin  of  variations  through  mechanical  stresses,  al- 
though he  seeks  for  the  origin  of  gemmules  through 

1  The  Law  of  Heredity,  Baltimore,  1883,  p.  80. 


HEREDITY  455 

the  lack  of  equilibrium  between  the  organization  and 
its  environment,  which  embraces  that  proposition 
without  definite  specification.  To  Weismann  we  are 
indebted  for  the  exposition  of  the  separate  origin  and 
relative  isolation  of  the  germ-plasma,  but  no  sufficient 
explanation  of  the  origin  and  inheritance  of  new  char- 
acters is  offered.  Ryder1  has  especially  dwelt  on  the 
physiological  division  of  labor  seen  in  the  tissues  of 
the  organism,  and  on  the  special  function  of  the  germ- 
plasma  as  the  recipient  of  impressions  through  the 
processes  of  metabolism  ;  but  he  does  not  go  into 
greater  detail. 

What  is  true  of  the  somatic  cells  is  also  true  of 
those  which  follow  immediately  the  segmentation  of 
the  oosperm.  Each  division  contains  the  entire  record, 
until  a  point  is  reached  in  which  specialization  of  its 
growth-capacities  begins. 

Dr.  Chalmers  Mitchell  thus  discusses  the  question 
as  to  the  location  of  specialized  growth  in  the  oosperm  :2 

"  Loeb  uses  the  term  heteromorphosis  to  denote 
the  power  of  organisms,  under  the  stimulus  of  outer 
conditions,  to  produce  organs  on  parts  of  the  organism 
where  they  do  not  occur  normally,  or  the  power  to  re- 
place lost  parts  by  parts  unsimilar  to  them.  Regenera- 
tion is  the  reproduction  of  like  parts.  Heteromorpho- 
sis is  the  reproduction  of  unlike  parts. 

;'If  one  cuts  off  part  of  the  stem  of  almost  any 
plant,  on  placing  the  stem  in  suitable  soil,  roots  will 
grow  out,  although  roots  are  not  natural  to  that  part 
of  the  stem.  The  prothallus  of  fern  produces  the  male 
and  female  organs  on  the  lower  side  turned  away  from 
the  light.  If  the  prothallus  be  darkened  on  the  upper 

1  American  Naturalist ,  1890,  p.  85. 

2  Natural  Science,  1894,  p.  187. 


456    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

surface,  and  illumined  by  reflected  light  on  the  lower 
surface,  then  the  antheridia  and  archegonia  will  be 
produced  on  the  upper  surface.  Galls  are  produced 
under  the  stimulus  of  the  insect  almost  anywhere  on 
the  surface  of  the  plant.  Yet  in  most  cases  these  galls, 
in  a  sense  grown  at  random  on  the  surface  of  a  plant, 
when  placed  in  damp  earth  will  give  rise  to  a  young 
plant.  In  the  hydroid,  Tubularia  mesembryanthemum, 
when  the  polyp-heads  are  cut  off,  new  heads  arise. 
But  if  both  head  and  root  be  cut  off,  and  the  upper  end 
be  inserted  in  the  mud,  then  from  the  original  upper 
end  not  head-polyps,  but  root-filaments,  will  arise, 
while  from  the  original  lower  end,  not  root-filaments, 
but  head-polyps  will  grow.  In  dona  intestinalis,  round 
a  slit  cut  into  the  body-wall,  a  tubular  process  grew  out, 
forming  a  new  mouth,  while  around  the  base  of  this,  a 
series  of  eye-spots,  corresponding  to  the  eye-spots 
round  the  real  mouth,  appeared.  In  all  these  cases, 
it  is  plain  that  there  were  present  in  parts  affected,  the 
determinants,  to  use  Weisrnann's  term,  not  only  of  the 
normal  parts,  but  also  of  parts,  which,  under  normal 
conditions,  would  never  have  appeared  there ;  and 
these  new  parts  growing  in  the  unwonted  places  bore 
the  normal  species-stamp  as  characteristically  as  sim- 
ilar parts  grown  in  their  normal  places.  It  can  hardly 
be  supposed  that  the  architecture  of  the  germ-plasm 
contains  special  determinants  to  be  ready  for  occur- 
rences so  casual,  especially  as  these  are  called  into 
existence  by  circumstances  quite  foreign  to  the  normal 
environment  of  the  organisms.  On  the  other  hand, 
the  facts  are  consonant  with  Hertwig's  belief  that,  as 
all  division  is  heirs-equal  division,  all  the  species- 
characters  that  depend  upon  cells  are  latent  in  every 
cell. 


HEREDITY.  457 

"The  experiments  of  Driesch,  Wilson,  and  Hert- 
wig  upon  the  early  stages  of  developing  ova  show  that 
heteromorphosis  begins  with  the  very  earliest  divisions 
of  the  egg.  Thus  Driesch,  working  upon  echinoderm 
embryos,  was  able  to  flatten  out  the  stage  where  there 
was  a  sphere  of  sixteen  cells  into  a  flat  plate  where  all 
the  cells  were  in  the  same  plane.  In  such  a  plate,  the 
nuclei  of  the  cells  occupied  relative  positions  very  dif- 
ferent from  the  normal  conditions.  Yet  from  these 
Driesch  obtained  normal  plutei  larvae.  It  was,  in  fact, 
as  if  the  cells  could  be  pushed  about  like  billiard  balls 
without  destroying  the  future  shape  and  characters  of 
the  embryo.  Did  each  cell  contain  only  the  determi- 
nants that  would  correspond  to  the  structures  that 
would  arise  from  it  under  normal  conditions  then 
change  of  its  normal  position  would  have  arrested  de- 
velopment. Each  cell  must,  on  the  other  hand,  have 
contained  the  determinants  for  all  the  animal,  and 
have  allowed  those  to  come  into  operation  that  were 
required  by  the  new  positions  into  which  the  cells  were 
forced.  Driesch,  by  separating  the  first  two  and  the 
first  four  segmentation-spheres  of  an  Echinus  ovum, 
obtained  two  or  four  normal  plutei,  respectively  one- 
half  and  a  quarter  of  the  normal  size.  Here  again 
each  sphere  must  have  contained  all  the  determinants 
for  the  whole  organism.  Heirs-equal  division  must 
have  occurred.  So,  also,  in  the  case  of  Amphioxus, 
Wilson  obtained  a  normal,  but  proportionately  dimin- 
ished, embryo  with  complete  nervous  system  from  a 
separated  sphere  of  a  two  or  four  or  eight-celled 
stage. 

"Hertwig  himself,  some  years  ago,  published  the 
results  of  experiments  he  made  upon  the  development 
of  frogs'  eggs  under  abnormal  conditions.  He  showed 


458    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

that  there  could  be  no  question  of  imperative  divisions 
separating  the  germ-plasm  into  right  and  left  halves, 
and  so  forth,  but  that  the  method  of  division  was  de- 
termined by  pressures  and  relative  gravities.  Altera- 
tion of  these  made  the  ova  divide  into  novel  but  sym- 
metrical forms.  Chabry  obtained  normal  embryos  in 
cases  where  some  of  the  segmentation-spheres  had 
been  artificially  destroyed. 

"These  cases  all  show  that  in  its  possibilities  each 
segmentation-sphere  is  identical ;  that  as  a  result  of 
heirs-equal  division,  each  cell  contains  all  the  material 
necessary  to  cause  the  development  of  a  complete  em- 
bryo. Weismann  would  have  to  suppose  that  in  all 
these  cases,  in  addition  to  its  half  of  the  nuclear  mat- 
ter resulting  from  heirs-equal  division,  it  had  also  a 
stock  of  unaltered  germ-plasm  ready  to  be  called  into 
activity  by  unwonted  stimuli.  But  even  this  hypothesis 
would  not  account  for  cells  distorted  by  compression 
responding  with  the  production  of  unwonted  symme- 
tries." 


6.   OBJECTIONS  TO  THE  DOCTRINE  OF  INHERITANCE 
OF  ACQUIRED  CHARACTERS. 

I  will  now  mention  some  objections  to  the  theory 
of  epigenesis,  or  the  inheritance  of  acquired  charac- 
ters. Some  of  them  appear  at  first  to  have  consider- 
able force,  but  the  explanations  which  have  been  of- 
fered seem  to  me  to  be  sufficient. 

Weismann's  merit  consists  in  having  directed  at- 
tention to  the  isolation  and  continuity  of  the  germ- 
plasma,  factors  which  must  be  taken  account  of  in  any 
theory  of  inheritance.  The  continuity  of  reproductive 
function  which  this  substance  displays  is  a  fact  of  great 


HEREDITY.  459 

interest,  and  one  which  has  given  rise  to  the  statement 
that  it  is  under  normal  conditions,  immortal. 

Isolation  of  the  germ-plasma  is  however  doubt- 
fully complete  anywhere,  and  in  the  vegetable  king- 
dom it  scarcely  exists.  Most  plants  may  be  propa- 
gated either  by  roots,  cuttings,  bulbs,  buds,  or  even 
by  leaves.  The  germ-plasma  is  evidently  as  widely 
distributed  in  these  multicellular  organisms,  as  it  is  in 
a  Protozoon.  The  greater  degree  of  isolation  exhib- 
ited by  the  higher  animals  is  one  of  their  many  spe- 
cializations, but  that  it  is  not  complete  is  shown  by  the 
facts  already  cited  in  the  preceding  pages.  The  con- 
tinuity of  protoplasm  in  the  organism  is  likely  to  be 
true  of  the  germ-cells  as  of  other  cells ;  and  they  are 
not  deprived  of  nutrition,  so  that  they  are  evidently 
accessible  to  influences  from  or  through  the  soma.  As 
regards  the  immortality  of  the  Protozoon  there  is  rea- 
son to  believe,  that  like  its  descendent  the  germ-cell, 
it  requires  renewal  from  another  cell  to  escape  death. 
According  to  Maupas,  the  Protozoa  after  reproducing 
by  self-division  for  many  generations,  require  conju- 
gation, or  they  dwindle  and  die: 

The  old  formula  that  variation  is  due  to  "natural 
selection  and  heredity"  has  derived  new  life  from  the 
fact  that  sexual  conjugation  is  necessary  for  the  re- 
newal of  the  vitality  of  the  ovarian  cell.  It  is  sup- 
posed by  Weismann  that  variation  as  well  as  repro- 
ductive energy  is  introduced  in  this  way,  the  process 
being  termed  by  him  Amphimixis.  But  like  the  old 
formula  this  explains  nothing,  for  if  the  parents  are 
the  sources  of  variation,  the  question  as  to  the  source 
of  the  variation  is  simply  relegated  to  the  parents  for 
answer.  Moreover,  Brooks,  who  made  this  suggestion 
prior  to  Weismann,  points  out  that  it  has  less  force 


460    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

than  appears  at  first  sight  to  belong  to  it.  He  shows1 
that  the  ancestors  of  the  individuals  of  a  given  species 
are  in  greater  or  less  degree  identical  persons,  and 
that  they  are  on  this  account  less  numerous  than  has 
been  sometimes  assumed.  Thus,  if  the  population  of 
a  given  district  had  for  ten  generations  married  first 
cousins,  the  total  ancestry  of  each  person  for  that 
period  would  number  only  thirty-eight  persons.  If, 
on  the  contrary,  all  the  ancestors  of  each  person  had 
been  distinct  individuals,  the  total  number  of  ances- 
tors in  ten  generations  would  be  two  thousand  and 
forty-six  persons.  An  investigation  into  the  ancestry 
of  three  persons,  not  nearly  related,  living  on  an  island 
on  the  Atlantic  coast  where  the  records  are  complete 
for  seven  and  eight  generations,  shows  that  the  ances- 
try of  each  of  the  three  averages  only  three  hundred 
and  eighty-two  persons.  That  this  consideration  is  of 
even  greater  importance  in  estimating  the  ancestry  of 
the  lower  animals  than  in  man,  is  evident  from  the 
fact  that  no  consideration  of  kinship  modifies  their  re- 
productive habits. 

The  fact  that  mutilations  are  not  generally  inherited 
is  cited  as  evidence  against  the  inheritance  of  acquired 
characters.  A  particular  mutilation,  however,  as  al- 
ready remarked,  rarely  happens  more  than  once  or 
twice  in  the  lifetime  of  a  single  individual;  in  fact  its 
occurrence  more  than  once  is,  in  many  cases,  as  in 
amputations,  impossible.  Such  sporadic  events  must 
necessarily  have  little  influence  as  stimuli  to  the  organ- 
ism, in  comparison  with  the  habitual  movements  of  ani- 
mals, or  the  continued  exposure  to  especial  physical 
conditions,  as  is  experienced  by  both  plants  and  ani- 
mals, and  are  not  worth  considering  in  this  connection. 

1  Science,  1895,  February,  p.  121. 


HEREDITY.  461 

One  of  the  cases  which  is  cited  in  opposition  to  the 
view  here  sustained,  is  the  alleged  fact  that  the  artifi- 
cial contraction  of  the  feet  undergone  by  high-caste 
Chinese  female  children,  resulting  in  deformity  of  the 
feet  of  the  women,  is  not  inherited.  That  this  abnor- 
mality has  never  been  transmitted  has  not  yet  been 
satisfactorily  shown  ;  but  in  any  case  there  are  some 
reasons  why  it  should  not  be  inherited.  One  of  these 
is,  that  the  deformity  is  confined  to  one  sex.  The 
male,  who  is  without  it,  has  the  advantage  of  an  an- 
cestry possessing  normal  feet  extending  backwards 
indefinitely,  while  the  modification  of  the  female  is  a 
very  modern  interference  with  the  law  of  the  species. 
Moreover,  a  positive  stimulus  to  ontogenetic  growth, 
such  as  is  in  this  instance  furnished  by  the  male,  is 
always  likely  to  be  prepotent  as  compared  with  the 
negative  part  played  by  the  female. 

Professor  Poulton,  whose  interesting  experiments 
kj^the  production  of  color  changes  in  lepidopterous 
larvSK  and  pupae  have  been  previously  cited,  states  that 
none  of  the  color  varieties  which  he  has  obtained,  have 
been  inherited.  I  cannot  regard  this  result  as  con- 
clusive until  the  experiments  have  been  continued  for 
a  longer  period  than  has  yet  been  possible  to  devote 
to  them. 

Perhaps  the  strongest  case  that  can  be  made  out 
against  the  theory  of  use-inheritance  as  defended  in 
the  present  book,  is  that  of  the  variety  of  structure 
displayed  by  the  neuter  members  of  the  colonies  of 
ants  and  termites.  Mr.  W.  P.  Ball  describes  these 
briefly  as  follows  : l 

"But  there  happens  to  be  a  tolerably  clear  proof 
that  such  changes  as  the  evolution  of  complicated 

1  The  Effects  of  Use  and  Disuse,  Nature  Series,  1890,  p.  24. 


462    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

structures  and  habits  and  social  instincts  can  take 
place  independently  of  use-inheritance.  The  wonder- 
ful instincts  of  the  working-bees  have  apparently  been 
evolved  (at  least  in  all  their  later  social  complications 
and  developments)  without  the  aid  of  use-inheritance — 
nay,  in  spite  of  its  utmost  opposition.  Working-bees, 
being  infertile  'neuters,'  cannot,  as  a  rule,  transmit 
their  own  modifications  and  habits.  They  are  de- 
scended from  countless  generations  of  queen-bees  and 
drones,  whose  habits  have  been  widely  different  from 
those  of  the  workers,  and  whose  structures  are  dissim- 
ilar in  various  respects.  In  many  species  of  ants  there 
are  two,  and  in  the  leaf-cutting  ants  of  Brazil  there 
are  three,  kinds  of  neuters  which  differ  from  each  other 
and  from  their  male  and  female  ancestors  'to  an  al- 
most incredible  degree.'1  The  soldier  caste  is  distin- 
guished from  the  workers  by  enormously  large  heads, 
very  powerful  mandibles,  and  extraordinarily  different 
instincts.  In  the  driver  ant  of  West  Africa  one  kind 
of  neuter  is  three  times  the  size  of  the  other,  and  has 
jaws  nearly  five  times  as  long.  In  another  case,  'the 
workers  of  one  caste  alone  carry  a  wonderful  sort  of 
shield  on  their  heads.'  One  of  the  three  neuter  classes 
in  the  leaf-cutting  ants  has  a  single  eye  in  the  midst  of 
its  forehead.  In  certain  Mexican  and  Australian  ants 


1  Origin  of  Species,  pp.  230-232  ;  Bates' s  Naturalist  an  the  Amazons.  Dar- 
win is  surprised  that  no  one  has  hitherto  advanced  the  demonstrative  case  of 
neuter  insects  against  the  well-known  doctrine  of  inherited  habit  as  advanced 
by  Lamarck.  As  he  justly  remarks,  "it  proves  that  with  animals,  as  with 
plants,  any  amount  of  modification  may  be  effected  by  the  accumulation  of 
numerous  slight,  spontaneous  variations,  which  are  in  any  way  profitable, 
without  exercise  or  habit  having  been  brought  into  play.  For  peculiar  habits 
confined  to  workers,  however  long  they  might  be  followed,  could  not  possibly 
affect  the  males  and  fertile  females,  which  alone  leave  any  descendants." 
Some  slight  modification  of  these  remarks,  however,  may  possibly  be  needed 
to  meet  the  case  of  "  factitious  queens,"  who  (probably  through  eating  par- 
ticles of  the  royal  food)  become  capable  of  producing  a  few  male  eggs. 


HEREDITY.  463 

some  of  the  neuters  have  high  spherical  abdomens, 
which  serve  as  living  reservoirs  of  honey  for  the  use  of 
the  community.  In  the  equally  wonderful  case  of  the 
termites,  or  so-called  'white  ants'  (which  belong,  how- 
ever, to  an  entirely  different  order  of  insects  from  the 
ants  and  bees),  the  neuters  are  blind  and  wingless, 
and  are  divided  into  soldiers  and  workers,  each  class 
possessing  the  requisite  instincts  and  structures  adapt- 
ing it  for  its  tasks.  Seeing  that  natural  selection  can 
form  and  maintain  the  various  structures  and  the  ex- 
ceedingly complicated  instincts  of  ants  and  bees  and 
wasps  and  termites  in  direct  defiance  of  the  alleged 
tendency  to  use-inheritance,  surely  we  may  believe 
that  natural  selection,  unsupported  by  use-inheritance, 
is  equally  competent  for  the  work  of  complex  or  social 
or  mental  evolution  in  the  many  cases  where  the  strong 
presumptive  evidence  cannot  be  rendered  almost  in- 
disputable by  the  exceptional  exclusion  of  the  modified 
animal  from  the  work  of  reproduction. 

"Ants  and  bees  seem  to  be  capable  of  altering  their 
habits  and  methods  of  action  much  as  men  do.  Bees 
taken  to  Australia  cease  to  store  honey  after  a  few 
years'  experience  of  the  mild  winters.  Whole  com- 
munities of  bees  sometimes  take  to  theft,  and  live  by 
plundering  hives,  first  killing  the  queen  to  create  dis- 
may among  the  workers.  Slave  ants  attend  devotedly 
to  their  captors  and  fight  against  their  own  species. 
Forel  reared  an  artificial  ant-colony  made  up  of  five 
different  and  more  or  less  hostile  species.  Why  can- 
not a  much  more  intelligent  animal  modify  his  habits 
far  more  rapidly  and  comprehensively  without  the  aid 
of  a  factor  which  is  clearly  unnecessary  in  the  case  of 
the  more  intelligent  of  the  social  insects." 

The  explanation  of  this  phenomenon  will  be  prob- 


464   PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

ably  some  day  found  by  paleontological  discovery. 
We  may  suppose,  on  the  basis  of  discoveries  already 
made  in  other  animals,  that  the  primitive  ants  and. 
termites  presented  homogeneous  colonies,  and  that 
the  varied  structures  which  they  present  to-day  have 
been  primarily  due  to  the  usual  process  of  specializa- 
tion through  use-inheritance.  It  is  necessary  to  sup- 
pose that  the  varied  functions  of  the  different  members 
of  the  community  have  modified  the  structures  of  the 
parts  essential  to  their  performance.  It  is  probable 
that  the  earliest  ants  in  an  early  geologic  period  be- 
came soldiers  under  the  usual  exigencies  of  their  strug- 
gle for  existence,  and  having  thus  secured  a  place  in 
the  economy  of  nature,  certain  members  of  the  com- 
munities underwent  degenerative  changes,  appropriate 
to  their  respective  functions,  of  a  less  exacting  charac- 
acter.  In  a  second  stage  of  evolution  the  community 
would  present  the  character  of  a  family  of  varied  forms 
all  of  whose  members  would  produce  any  or  all  of  the 
types  of  form  to  be  found  in  it,  under  slight  diversi- 
ties of  conditions,  just  as  now,  all  species  produce 
young  of  two  sexes.  The  differences  between  the 
members  of  an  ant  community  are  considerable  in  ap- 
pearance, but  not  so  great  essentially  as  that  between 
sexes. 

Finally,  in  a  third  stage  of  the  history,  the  func- 
tions of  reproduction  come  to  be  the  special  office  of 
a  few  members  of  the  community.  This  may  have 
been  due  to  starvation,  or  to  excessive  labor  on  the 
part  of  certain  individuals  aborting  the  reproductive 
powers;  but  whatever  may  have  been  the  cause,  a 
majority  of  individuals  became  sterile.  The  repro- 
ducing members  of  the  community,  however,  have 
continued  to  produce  all  the  forms  of  the  community. 


HEREDITY.  465 

They  produce  sterile  workers  and  soldiers,  sometimes 
of  several  forms,  although  themselves  unlike  most  of 
their  progeny.  ''This,"  says  Mr.  Ball,  "  is  evidence 
that  inheritance  can  have  no  share  in  the  process."  He 
believes  that  each  one  of  the  structural  types  of  the 
community  is  produced  by  the  treatment  accorded  to 
the  young  by  the  workers,  each  generation  for  itself. 

As  we  have  seen  that  the  embryonic  and  paleonto- 
logic  histories  distinctly  negative  the  idea  that  each 
generation  has  been  produced  by  itself  without  inheri- 
tance, let  us  endeavor  to  read  the  riddle  in  the  light 
of  the  knowledge  we  have  gained  from  paleontology. 
I  assume  that  the  most  specialized  types,  the  soldiers, 
represent  the  type  of  the  species  in  Mesozoic  and  pos- 
sibly earlier  time.  They  are  already  known  from  early 
Cenozoic  formations  (Scudder).  The  process  of  change 
into  workers  and  breeders  has  been  degenerative.  I 
suppose,  however,  that  in  ants,  as  in  the  case  of  many 
other  animals,  slight  differences  in  the  supply  of  nutri- 
tive energy  will  prevent  or  produce  these  degenerative 
processes,  as  it  appears  to  do  in  the  case  of  the  pro- 
duction of  the  sexes.  (Experiments  on  lepidopterous 
larvae  have  shown  that  excessive  food  supply  produces 
females,  and  deficient  supply  produces  males).  In 
bees  the  larvae  of  the  female  (queen)  receives  the  larg- 
est food  supply  ;  those  of  the  males  less  ;  and  those  of 
the  neuters  the  least  of  all.  How  the  food  supply 
came  to  be  varied  so  as  to  produce  the  several  types 
in  accordance  with  the  exigencies  of  the  community, 
is  a  question  to  be  solved  by  future  research.  Perhaps 
it  was  due  to  variations  in  the  supplies  available  at 
particular  times  of  the  year ;  and  perhaps  the  ants  ul- 
timately learned  the  secret,  and  now  practice  it  intelli- 
gently. It  is  enough  for  my  present  purpose  to  have 


466   PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

shown  that  the  basis  of  the  entire  community,  the  most 
specialized  form,  the  original  fertile  soldier,  acquired 
his  characters  in  the  usual  way,  by  use,  and  that  all 
other  forms  have  been  derived  from  him  by  inheritance 
modified  by  disuse,  or  degeneracy,  under  the  influence 
of  variations  in  the  food  supply. 

This  reply  to  Mr.  Ball's  argument  was  made  by 
me  at  a  meeting  of  the  Philadelphia  Academy  of  Nat- 
ural Sciences  on  May  23,  1893.  In  the  latter  part  of 
the  same  year  an  almost  identical  answer  was  pub- 
lished by  Herbert  Spencer.  My  remarks  were  not  pub- 
lished until  the  end  of  the  year. 

Mr.  A.  R.  Wallace1  presents  the  fact  of  change  of 
character  under  external  stimulus  as  evidence  of  the 
non-inheritance  of  acquired  characters.  Thus  he  cites 
the  cases  of  change  of  species  of  Artemia,  in  conse- 
quence of  increased  salinity  of  water  Cantea,  p.  229)  ; 
and  of  the  change  of  color  of  a  Texan  Saturnia,  when 
its  normal  food-plant  Juglans  nigra  was  replaced  by 
/.  regia.  Under  the  new  conditions  the  old  characters 
were  not  continued.  In  the  same  way  the  appearance 
of  all  new  characters  might  be  assumed  to  prove  non- 
inheritance  of  the  old  ones.  The  obvious  interpretation 
of  these  facts  is  the  one  generally  given  them  ;  that  is, 
they  demonstrate  the  superior  potency  of  certain  new 
stimuli  over  the  inherited  type  of  growth- energy.  They 
demonstrate  that  the  energy  of  inheritance  is  not  un- 
changeable in  its  type,  which  is  the  condition  of  the 
possibility  of  evolution.  They  do  not  demonstrate 
that  acquired  characters  cannot  be  inherited. 

Objections  have  been  made  to  the  supposition  that 
the  simian  characters  of  the  lower  human  races  are 
due  to  inheritance  because  it  has  been  shown  that 

^Nature,  1893,  p.  267. 


HEREDITY.  467 

some  of  them  are  due  to  mechanical  causes  acting 
after  birth. 

The  demonstration  of  the  mechanical  origin  of  a 
given  peculiarity,  however,  by  no  means  precludes 
that  such  peculiarity  may  not  be  an  inheritance  from 
or  reversion  to  pithecoid  ancestors.  It  has  been  al- 
ready pointed  out  that  all  of  the  form  characters  of 
the  vertebrate  skeleton,  and  for  that  matter,  of  the 
hard  parts  of  all  animals,  have  been  produced  by  mus- 
cular pressures  and  contractions,  and  the  friction, 
strains,  and  impacts,  due  to  these.  The  demonstra- 
tions by  Virchow  and  others  that  such  is  the  origin  of 
the  platycnemic  human  tibia,  is  directly  in  the  line  of 
Neo-Lamarckian  evolutionary  doctrine,  and  shows  us 
that  atavistic  and  reversionary  characters  are  found  in 
the  muscular  system  as  well  as  in  the  skeleton.  Such 
characters  are  inheritable  as  well  as  those  of  the  skel- 
eton. But  the  characters  of  the  skeleton  can  generally 
be  shown  to  be  inherited,  because  they  appear  before 
birth,  and  are  found  at  some  stage  or  another  of  foetal 
life.  The  later  appearance  of  the  muscular  structures 
in  the  ontogeny,  is  simply  a  case  of  caenogeny,  where 
the  record  has  been  falsified  by  retardation  of  the  parts 
in  question. 

The  variations  in  the  characters  of  the  human  skel- 
eton are  of  very  various  significance  and  value,  and 
the  zoologist  and  paleontologist  can  perceive  that  they 
are  sometimes  misinterpreted  by  archeologists.  Thus 
the  presence  of  wormian  (Inca)  bones,  and  of  a  per- 
foration of  the  olecranar  fossa,  have  no  zoological 
value  ;  while  the  prognathous  jaws,  tritubercular  mo- 
lar, and  platycnemic  tibia  have  such  a  value.  The 
tufted  hair  of  the  negro  has  a  human  value  only,  as  it 
does  not  occur  in  any  of  the  Quadrumana.  But  arche- 


468     PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

ologists  who  are  not  zoologists  are  not  careful  to  point 
out  these  distinctions. 

If  the  platycnemic  tibia  has  been  produced  by  mus- 
cular pressure  in  man,  it  has  been  probably  so  pro- 
duced in  the  apes,  where  it  is  a  universal  character. 
If  the  early  fusion  of  the  sagittal  suture  is  produced 
by  the  vigorous  contractions  of  the  temporal  muscle 
as  suggested  by  Brinton,  in  the  black  race,  due  to 
prognathous  jaws,  this  is  probably  why  it  is  a  universal 
character  of  the  apes,  where  the  jaws  are  still  more 
prognathous.  What  may  be  the  cause  of  prognathism 
is  not  explained  by  archeologists,  but  has  been  dis- 
cussed in  my  book  on  the  Origin  of  the  Fittest,  and  by 
Dr.  C.  S.  Minot.  That  the  prognathous  jaws  and 
platycnemic  tibia  are  not  found  in  the  foetus  by  no 
means  proves  that  they  are  not  inherited  characters. 
Besides  the  fact  already  mentioned,  that  we  are  by 
this  only  thrown  back  on  an  inherited  muscular  struc- 
ture, it  is  further  to  be  remarked  that  characters  which 
indicate  the  evanescence  or  degeneracy  of  parts,  do 
not  usually  appear  in  the  foetus,  but  are  disclosed  at 
later  stages.  The  prognathous  jaws  are  disappearing 
from  the  higher  races,  and  the  process  of  disappear- 
ance is  in  this  point  accomplished  by  a  retention  of 
the  foetal  face,  which  is  excessively  orthognathous. 
Prognathism  is  characteristic  of  most  of  the  lower 
Mammalia,  and  whenever  man  displays  it,  if  he  be,  as 
evolutionists  believe,  descended  from  some  other  mam- 
mal, he  is  simply  continuing  to  develop  the  old  char- 
acter in  the  old  manner.  The  same  reasoning  applies 
to  the  platycnemic  tibia  and  the  tritubercular  molar. 

As  regards  the  lemurine  character  of  the  trituber- 
cular molar,  the  term  is  a  good  one,  as  indicating  the 
nearest  of  kin  to  man  which  present  such  molars.  But 


HEREDITY.  469 

this  type  can  with  equal  propriety  be  called,  as  I  have 
shown,  the  primitive  placental  molar.  The  lemur  is 
the  highest  form  next  to  man  which  displays  it,  but  it 
was  universal  among  the  placentals  at  one  geological 
epoch.  It  is  possible  that  Topinard's  suggestion  as 
to  the  cause  of  its  appearance  in  man  is  the  correct 
one,  as  I  made  the  same  many  years  before,  but  that 
does  not  affect  its  value  as  an  evidence  of  reversion, 
as  in  the  cases  already  cited.  There  are  various  other 
ways  in  which  molar  teeth  may  degenerate,  besides 
reversion  to  trituberculy,  with  which  dentists  are  fa- 
miliar, and  which  may  be  explained  as  Topinard  and 
I  have  done  ;  i.  e.,  by  change  of  food;  but  why  the 
regular  and  normal  mode  should  be  trituberculy,  and 
not  one  of  those  other  modes,  requires  additional  ex- 
planation. This  explanation  is  that  a  regular  or  nor- 
mal retrogressive  modification  of  a  structure  is  likely 
to  be  a  return  on  the  line  by  which  it  advanced.  This 
is  atavism  or  reversion. 

That  the  anthropoids  have  been  directly  derived 
by  descent  from  the  false  lemurs  rather  than  from  the 
Old  World  monkeys  (Cercopithecidae)  is  probable  for 
various  reasons  which  I  have  pointed  out  on  page  157. 
I  mention  now  that  this  view  is  somewhat  confirmed 
by  the  recent  discovery  by  Forsyth-Major,  in  Mada- 
gascar, in  beds  of  Plistocene  age,  of  a  skull  of  a  new 
genus  of  Lemuridae  with  tritubercular  molars,  whose 
single  species  is  nearly  as  large  as  a  chimpanzee. 

In  closing  these  remarks,  I  call  attention  to  the 
frequent  muscular  and  occasional  cerebral  anomalies 
found  in  the  negro,  which  are  of  simian  character,  and 
which  indicate  simian  descent.  An  excellent  synopsis 
of  these  has  been  given  by  Dr.  Frank  Baker  in  his 
address  at  Cleveland  in  1888  as  Vice-President  of  the 


470     PRIMAR  Y  FA  CTORS  OF  ORGANIC  E VOL  UTION. 

American  Association  for  the  Advancement  of  Science, 
and  by  Prof.  H.  F.  Osborn  in  1891  in  the  Cartwright 
lecture  before  the  New  York  College  of  Physicians. 

It  is  evident  that  evolutionists  are  reaching  greater 
harmony  of  opinion  on  the  question  of  inheritance. 
In  fact,  the  discussion  is  sometimes  a  logomachy  de- 
pendent on  the  significance  which  one  attaches  to 
the  term  "acquired  characters."  Thus  Von  Rath1  re- 
marks :  "There  is  nothing  in  the  way  of  the  opinion 
that  by  the  continued  working  of  such  external  in- 
fluences and  stimuli  the  molecular  structure  of  the 
germ-plasma  also  experiences  a  change  which  can  lead 
to  a  transmission  of  transformations.  Above  all,  it 
ought  not  to  be  forgotten  in  this  case  that  the  somatic 
cells  are  in  no  way  the  first  to  be  modified  by  the  stim- 
ulus, and  that  then  by  some  sort  of  unexplained  pro- 
cess (pangenesis  or  intracellular  pangenesis),  this 
stimulus  is  transmitted  gradually  by  these  cells  to  the 
plasma  of  the  germ-cells.  The  influence  on  the  germ- 
plasm  is  rather  a  direct  one,  and  if  by  continued  in- 
fluence a  transformation  of  the  structure  of  this  plasm 
takes  place  and  transmission  occurs,  we  have  then 
simply  a  transmission  of  blastogenic,  and  by  no  means 
of  somatogenic  characters,  and  therein  is  not  the 
slightest  admission  of  the  transmission  of  acquired 
characters." 

This  paragraph  contains  an  admission  of  the  doc- 
trine of  diplogenesis,  and  does  not  regard  the  phe- 
nomena as  including  a  transmission  of  acquired  char- 
acters. Nevertheless  the  stimuli  traverse  the  soma  in 
order  to  reach  the  germ-plasma.  Such  an  energy  is 
evidently  then  not  of  blastogenic  origin,  although  it  is 

IBerichte  der  naturforschenden  Gcsellschaft  zu  Freiburg  in  Baden,  Bd.VI., 
Heft  3. 


HEREDITY.  471 

such  in  its  effects.  Moreover,  Von  Rath  omits  to  men- 
tion the  fact  that  in  traversing  the  soma,  the  stimulus, 
frequently,  if  not  always,  produces  effects  on  the  latter 
similar  to  those  which  it  produces  on  the  germ-plasma. 
I  should  call  this  process  the  inheritance  of  an  acquired 
character,  even  in  the  case  where  no  corresponding 
modification  appears  in  the  soma,  since  the  causative 
energy  is  acquired  by  the  soma  and  is  not  derived  from 
the  existing  germ-plasma. 

Romanes1  says,  in  reviewing  the  opinions  of  Weis- 
mann :  "  (i)  Germ-plasm  ceases  to  be  continuous  in 
the  sense  of  having  borne  a  perpetual  record  of  con- 
genital variations  from  the  first  origin  of  sexual  propa- 
gation. (2)  On  the  contrary,  as  all  such  variations  have 
been  originated  by  the  direct  action  of  external  conditions 
[italics  mine],  the  continuity  of  the  germ-plasm  in  this 
sense  has  been  interrupted  at  the  commencement  of 
every  inherited  change  during  the  phylogeny  of  all 
plants  and  animals,  unicellular  as  well  as  multicellular. 
(3)  But  germ-plasm  remains  continuous  in  the  re- 
stricted though  highly  important  sense  of  being  the 
sole  repository  of  hereditary  characters  of  each  succes- 
sive generation,  so  that  acquired  characters  can  never 
have  been  transmitted  to  progeny  ' representatively,' 
even  though  they  have  frequently  caused  those  'spe- 
cialized '  changes  in  the  structure  of  germ-plasm,  which 
as  we  have  seen,  must  certainly  have  been  of  con- 
siderable importance  in  the  history  of  organic  evolu- 
tion." 

Here  the  inheritance  of  characters  acquired  by  the 
soma  is  admitted,  and  the  process  is  after  the  method 
of  diplogenesis.  According  to  Romanes,  Galton  origin- 

lAn  Examination  of  IVeismannism,  Chicago,  1893,  p.  169. 


472    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

ally  propounded  this  doctrine.  Galton's  language1  is 
as  follows : 

"It  is  said  that  the  structure  of  an  animal  changes 
when  he  is  placed  under  changed  conditions;  that  his 
offspring  inherit  some  of  his  change ;  and  that  they 
vary  still  further  on  their  own  account,  in  the  same 
direction,  and  so  on  through  successive  generations 
until  a  notable  change  in  the  congenital  characteristics 
of  the  race  has  been  effected.  Hence,  it  is  concluded 
that  a  change  in  the  personal  structure  has  reacted  on 
the  sexual  elements.  For  my  part,  I  object  to  so  gen- 
eral a  conclusion,  for  the  following  reasons.  It  is 
universally  admitted  that  the  primary  agents  in  the 
processes  of  growth,  nutrition,  and  reproduction,  are 
the  same,  and  that  a  true  theory  of  heredity  must  so 
regard  them.  In  other  words,  they  are  all  due  to  the 
development  of  some  germinal  matter,  variously  lo- 
cated. Consequently,  when  similar  germinal  matter 
is  everywhere  affected  by  the  same  conditions,  we 
should  expect  that  it  would  be  everywhere  affected  in 
the  same  way.  The  particular  kind  of  germ  whence 
the  hair  sprang,  that  was  induced  to  throw  out  a  new 
variety  in  the  cells  nearest  to  the  surface  of  the  body 
under  certain  changed  conditions  of  climate  and  food, 
might  be  expected  to  throw  out  a  similar  variety  in  the 
sexual  elements  at  the  same  time.  The  changes  in 
the  germs  would  everywhere  be  collateral,  although 
the  movements  where  any  of  the  changed  germs  hap- 
pen to  receive  their  development  might  be  different." 

This  is  the  first  statement  of  the  doctrine  of  diplo- 
genesis  with  which  I  have  met,  and  it  appears  to  fur- 
nish the  most  rational  basis  for  the  investigation  into 
the  dynamics  of  the  process. 

1  Contemporary  Review,  1875,  pp.  343-344 ;  Proc.  Royal  Society,  1872,  No.  136. 


CHAPTER  IX.— THE  ENERGY  OF 
EVOLUTION. 


IF  we  view  the  phenomena  of  organic  life  from  the 
standpoint  of  the  physicist,  the  first  question  that 
naturally  arises  in  the  mind  is  as  to  the  kind  of  energy 
of  which  it  is  an  exhibition.  Ordinary  observation 
shows  that  organic  bodies  perform  molar  movements, 
and  that  many  of  them  give  out  heat.  A  smaller  num- 
ber exhibit  emanations  of  light  and  electricity.  Very 
little  consideration  is  sufficient  to  show  that  they  in- 
clude among  their  functions  chemical  reactions,  a  con- 
viction which  is  abundantly  sustained  by  researches 
into  the  physiology  of  both  animals  and  plants.  The 
phenomena  of  growth  are  also  evidently  exhibitions  of 
energy.  The  term  energy  is  used  to  express  the  mo- 
tion of  matter,  and  the  building  of  an  embryo  to  ma- 
turity is  evidently  accomplished  by  the  movement  of 
matter  in  certain  definite  directions.  The  energy  which 
accomplishes  this  feat  is,  however,  none  of  those  which 
characterize  inorganic  matter,  some  of  which  have  just 
been  mentioned,  but,  judging  from  its  phenomena,  is 
of  a  widely  different  character.  If  we  further  take  a 
broad  view  of  the  general  process  of  progressive  evo- 
lution, which  is  accomplished  by  successive  modifica- 
tions of  this  growth-energy,  we  see  further  reason  for 


474    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

distinguishing  it  widely  from  the  inorganic  energies. 
In  considering  the  dynamics  of  organic  evolution, 
it  will  be  convenient  to  commence  by  considering  the 
claims  of  natural  selection  to  include  the  energy  which 
underlies  the  process.  That  natural  selection  cannot 
be  the  cause  of  the  origin  of  new  characters,  or  varia- 
tion, was  asserted  by  Darwin  ;l  and  this  opinion  is 
supported  by  the  following  weighty  considerations  : 

1.  A  selection  cannot  be  the  cause  of  those  alterna- 
tives from  which  it  selects.     The  alternatives  must  be 
presented  before  the  selection  can  commence. 

2.  Since  the  number  of  variations  possible  to  or- 
ganisms is  very  great,  the  probability  of  the  admirably 
adaptive  structures  which  characterize   the  latter  hav- 
ing arisen  by  chance,  is  extremely  small. 

3.  In  order  that  a  variation  of  structure  shall  sur- 
vive, it  is  necessary  that  it  shall  appear  simultaneously 
in  two  individuals  of  opposite  sex.     But  if  the  chance 
of  its  appearing  in  one  individual  is  very  small,  the 
chance  of  its  appearing  in  two  individuals  is  very  much 
smaller.     But  even  this  concurrence  of  chances  would 
not  be  sufficient  to  secure  its  survival,  since  it  would 
be  immediately  bred  out  by  the  immensely  preponder- 
ant number  of  individuals  which  should  not  possess 
the  variation. 

4.  Finally,  the  characters  which  define  the  organic 
types,  so  far  as  they  are  disclosed  by  paleontology, 
have  commenced  as  minute  buds  or  rudiments,  of  no 
value  whatever  in  the  struggle  for  existence.     Natural 
selection  can  only  effect  the  survival  of  characters  when 
they  have  attained  some  functional  value. 

In  order  to  secure  the  survival  of  a  new  character, 
that  is,  of  a  new  type  of  organism,  it  is  necessary  that 

1  Origin  of  Species,  Ed.  1872,  p.  65. 


THE  ENERGY  OF  EVOLUTION.  475 

the  variation  should  appear  in  a  large  number  of  indi- 
viduals coincidentally  and  successively.  It  is  exceed- 
ingly probable  that  that  is  what  has  occurred  in  past 
geologic  ages.  We  are  thus  led  to  look  for  a  cause 
which  affects  equally  many  individuals  at  the  same 
time,  and  continuously.  Such  causes  are  found  in  the 
changing  physical  conditions  that  have  succeeded  each 
other  in  the  past  history  of  our  planet,  and  the  changes 
of  organic  function  necessarily  produced  thereby. 


i.  ANAGENESIS. 

It  is  customary  to  distinguish  broadly  between  in- 
organic and  organic  energies,  as  those  which  are  dis- 
played by  non-living  and  living  bodies.  This  classifi- 
cation is  inexact,  since,  as  already  remarked,  nearly 
all  of  the  inorganic  energies  are  exhibited  by  living 
beings.  A  division  which  appears  to  be,  with  our 
present  knowledge,  much  more  fundamental,  is  into 
the  energies  which  tend  away  from,  and  those  which 
tend  toward,  the  phenomena  of  life.  In  other  words, 
those  which  are  not  necessarily  phenomena  of  life,  and 
those  which  are  necessarily  such.  And  the  phenom- 
ena of  life  here  referred  to  are  the  phenomena  of  growth 
and  evolution,  as  distinguished  from  all  others.  I  have 
termed1  these  classes  the  Anagenetic,  which  are  ex- 
clusively vital,  and  the  Catagenetic,  which  are  phys- 
ical and  chemical.  The  anagenetic  class  tends  to  up- 
ward progress  in  the  organic  sense  ;  that  is,  toward 
the  increasing  control  of  its  environment  by  the  organ- 
ism, and  toward  the  progressive  development  of  con- 
sciousness and  mind.  The  catagenetic  energies  tend 
to  the  creation  of  a  stable  equilibrium  of  matter,  in 

1  The  Monist,  Chicago,  1893,  p.  630. 


476    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

which  molar  motion  is  not  produced  from  within,  and 
sensation  is  impossible.  In  popular  language  the  one 
class  of  energies  tends  to  life ;  the  other  to  death. 

Herbert  Spencer  has  defined  evolution  as  a  process 
of  "integration  of  matter  and  dissipation  of  motion";1 
"the  absorption  of  motion  and  the  diffusion  of  matter" 
he  terms  dissolution.  If  by  evolution  Mr.  Spencer 
referred  only  to  that  of  inorganic  bodies  and  masses, 
his  definition  must  be  accepted  ;  but  the  evolution  of 
organic  bodies,  since  it  has  proceeded  in  a  direction 
the  opposite  of  the  inorganic,  cannot  be  so  character- 
ized. Organic  evolution  has  passed  beyond  the  do- 
main of  the  inorganic,  and  the  terms  applicable  to  the 
latter  process  cannot  be  correctly  applied  to  the  former. 
In  organic  anagenesis  there  is  absorption  of  energy; 
dissipation  of  energy  is  only  known  in  the  functioning 
of  organic  structures,  which  is  catagenetic ;  not  in 
their  progressive  evolution,  which  is  anagenetic. 

Huxley,  in  a  lecture  delivered  in  I&54,2  remarks  : 
"Tendency  to  equilibrium  of  force  and  permanency  of 
form  then  are  the  characters  of  that  portion  of  the 
universe  which  does  not  live,  the  domain  of  the  chem- 
ist and  the  physicist.  Tendency  to  disturb  existing 
equilibriums,  to  take  on  forms  which  succeed  one 
another  in  definite  cycles,  is  the  character  of  the  living 
world."  In  the  letter  to  Professor  Tyndall,  prefatory 
to  the  volume  Lay  Sermons  and  Addresses,  in  which  this 
essay  appeared,  Huxley  says:  "The  oldest  essay  of 
the  whole,  that  on  '  The  Educational  Value  of  the 
Natural  History  Sciences,'  contains  a  view  of  the  dif- 
ferences between  living  and  not-living  bodies,  which  I 
have  long  since  outgrown."  Whatever  might  have 

1  First  Principles,  ed.  II.,  1873,  p.  542. 

2  Lay  Sermons  and  Addresses,  1880,  p.  75. 


THE  ENERGY  Of  EVOLUTION.  477 

been  the  cause  of  this  change  of  opinion  in  Huxley's 
mind,  the  cause  which  has  produced  a  similar  change 
in  the  minds  of  many  men,  has  been  the  discovery  of 
means  of  producing  in  the  laboratory  numerous  organic 
compounds,  which,  it  had  been  previously  supposed, 
could  not  be  produced  excepting  through  the  action  of 
living  things,  vegetable  and  animal.  But  it  has  been 
shown  that  all  of  these  substances  are  the  result  of  the 
running  down  of  protoplasm,  and  are,  hence,  catage- 
netic,  and  not  anagenetic. 

That  the  catagenetic  energies,  whether  physical  or 
chemical,  tend  away  from  life  is  clear  enough.  Thus 
molar  motion,  unless  continuously  supplied,  or  directed 
by  a  living  source,  speedily  ceases,  being  converted  by 
friction  into  heat,  which  is  dissipated.  The  same 
is  true  of  molecular  movements,  under  the  same  con- 
ditions. Chemical  reactions,  which  are  fundamental 
in  world-building,  result  in  the  production  of  solids 
and  the  radiation  of  heat.  This  is  the  general  result, 
although  in  the  process,  as  it  occurs  in  nature,  irregu- 
larities occur,  owing  to  local  and  temporary  elevation 
of  temperature.  This  arises  from  the  decomposition 
of  organic  substances,  which  liberates  heat ;  the  oxy- 
dization  of  carbon,  which  owes  its  position  as  a  ter- 
restrial element  to  vegetable  and  animal  organisms  ; 
and  the  access  of  heat  from  the  interior  of  the  earth, 
or  from  the  sun's  rays.  Finally  cosmic  creation  in- 
volves the  perpetual  radiation  of  heat  into  space,  and 
the  gradual  reduction  of  all  forms  of  matter  to  the 
solid  state. 

The  endothermic  chemical  reaction,  where  inor- 
ganic matter  undergoes  a  change  of  molecular  aggre- 
gation the  reverse  of  that  just  mentioned,  with  the  ab- 
sorption of  heat,  as  in  the  case  of  several  nitrogen 


478    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

compounds,  is  rare  in  nature,  where  free  from  organic 
complications,  and  is  necessarily  soon  reversed  by 
further  reactions. 

In  the  anagenetic  energies,  on  the  other  hand,  we 
have  a  process  of  building  machines,  which  not  only 
resist  the  action  of  catagenesis,  but  which  press  the 
catagenetic  energies  into  their  service.  In  the  assimi- 
lation of  inorganic  substances  they  elevate  them  into 
higher,  that  is  more  complex  compounds,  and  raise 
the  types  of  energy  to  their  own  level.  In  the  devel- 
opment of  molar  movements  they  enable  their  organ- 
isms to  escape  many  of  the  destructive  effects  of  cat- 
agenetic energy,  by  enabling  them  to  change  their 
environment;  and  this  is  especially  true  in  so  far  as  sen- 
sation or  consciousness  is  present  to  them.  The  ana- 
genetic  energy  transforms  the  face  of  nature  by  its 
power  of  assimilating  and  recompounding  inorganic 
matter,  and  by  its  capacity  for  multiplying  its  individ- 
uals. In  spite  of  the  mechanical  destructibility  of  its 
physical  basis  (protoplasm),  and  the  ease  with  which 
its  mechanisms  are  destroyed,  it  successfully  resists, 
controls,  and  remodels  the  catagenetic  energies  for  its 
purposes. 

The  anagenetic  power  of  assimilation  of  the  inor- 
ganic substances  is  chiefly  seen  in  the  vegetable  king- 
dom. Atmospheric  air,  water,  and  inorganic  salts 
furnish  it  with  the  materials  of  its  physical  basis.  Then 
from  its  own  protoplasm  it  elaborates  by  a  catagenetic 
retrograde  metamorphosis,  the  non-nitrogenous  sub- 
stances, as  wood  (cellulose),  waxes,  and  oils,  and  the 
nitrogenous  alkaloids,  and  it  may  take  up  inorganic 
substances  and  deposit  them  without  alteration  in  its 
cells.  Many  of  the  compounds  elaborated  by  plants 
and  animals  have  been  manufactured  of  latter  time  by 


THE  ENER  GY  OF  E  VOL  UTION.  4  79 

chemists.  The  discovery  that  the  living  organism  is 
not  necessary  for  the  production  of  these  substances 
has  led  to  the  hasty  conclusion  that  the  supposed  dis- 
tinction between  "organic"  and  "inorganic"  energy 
does  not  exist.  But  the  elaboration  of  these  substances 
is  not  accomplished  by  anagenetic  or  "vital"  energy, 
but  by  a  process  of  running  down  of  the  higher  com- 
pound protoplasm,  which  is  catagenesis.  No  truly 
anagenetic  process  has  yet  been  imitated  by  man. 

All  forms  of  functioning  of  organs,  except  assimi- 
lation, reproduction,  and  growth,  are  catagenetic.  That 
is,  functioning  consists  in  the  retrograde  metamorpho- 
sis of  a  nitrogenous  organic  substance  or  proteid  with 
the  setting  free  of  energy.  The  proteid  is  decomposed 
in  the  functioning  tissue  into  carbon  dioxide,  water, 
urea,  etc.,  and  energy  appears  in  the  muscle  as  con- 
traction, in  the  glands  as  secretion,  and  in  all  parts  of 
the  body  as  heat.  The  general  result  of  physiologic 
research  is,  that  the  decomposition  of  the  blood  is  the 
source  of  energy,  while  the  tissue  of  each  organ  deter- 
mines the  character  of  that  energy.  That  the  tissue 
itself  suffers  from  wear,  and  requires  repair,  is  also 
true,  but  to  a  less  extent  than  was  once  supposed. 

In  the  anagenetic  process  of  the  growth  of  the  em- 
bryo the  case  is  different.  Here  the  processes  of  func- 
tioning of  organs  are  in  complete  abeyance,  the  plasma 
of  the  oosperm  is  not  sensibly  broken  down  in  chemical 
decomposition,  but  it  is  in  great  part  elaborated  into 
tissues  and  organs.  All  the  mechanisms  necessary  to 
the  mature  life  of  the  individual  are  constructed  by  the 
activity  of  the  special  form  of  energy  known  as  growth- 
energy  or  Bathmism.  It  is  the  modifications  of  this 
energy  which  constitute  evolution,  and  it  is  these  to 
which  we  will  hereafter  direct  our  attention.  Its  sim- 


480    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

plest  exhibition  is  the  subdivision  of  a  unicellular  pro- 
toplasmic body  into  two  or  more  individuals  or  struc- 
tural units  of  a  multicellular  organism.  Further  divi- 
sion of  the  latter  does  not  abolish  the  individual,  but 
extends  it,  and  we  now  observe  the  elaboration  of  dif- 
ferent structural  types  to  become  the  conspicuous  func- 
tion of  this  form  of  energy.  In  other  words,  a  once 
simple  energy  becomes  specialized  into  specific  ener- 
gies, each  of  which,  once  established,  pursues  its  mode 
of  motion  in  opposition  to  all  other  modes  not  more 
potent  than  itself.  Besides  the  evident  truth  of  the 
proposition  that  a  mode  of  building  is  a  mode  of  mo- 
tion, we  have  another  very  good  reason  for  believing 
in  the  existence  of  a  class  of  bathmic  or  growth-ener- 
gies. This  is  found  in  the  phenomena  of  heredity. 
The  most  rational  conception  of  this  inheritance  of 
structural  characters  is  the  transmission  of  a  mode  of 
motion  from  the  soma  to  the  germ-cells.  This  is  a  far 
more  conceivable  method  than  that  of  the  transmis- 
sion of  particles  of  matter,  other  than  the  ordinary  ma- 
terial of  nutrition.  The  bathmic  theory  of  heredity 
bears  about  the  same  relation  to  a  theory  of  transmis- 
sion of  the  pangenes  of  Darwin,  or  the  ids  of  Weis- 
mann,  as  the  undulatory  theory  of  light  and  other 
forms  of  radiant  energy  does  to  the  molecular  theory 
of  Newton.  I  have  therefore  assumed  as  a  working 
hypothesis  the  existence  of  the  bathmic  energy,  and 
have  inquired  how  far  the  facts  in  our  possession  sus- 
tain it.  In  doing  so  it  has  been  necessary  to  elaborate 
the  theory  so  as  to  render  clearer  its  application  to  spe- 
cific cases.  The  fact  to  be  accounted  for  is  its  spe- 
cialization into  so  many  diverse  specific  forms. 

A  further  indication  of  the  existence  of  the  bathmic 
energy  is  the  quantitative  limitation   to  which  growth 


THE  ENERGY  OF  EVOLUTION.  481 

is  obedient.  Thus  the  successive  stages  of  embryonic 
growth  are  limited  in  number  in  each  species.  The 
dimensions  of  most  species  are  limited  within  a  def- 
inite range.  The  duration  of  life,  or  of  the  functioning 
organic  machine,  has  a  definite  limit  in  time.  All  this 
means  that  a  certain  limited  quantity  of  energy  is  at 
the  disposal  of  each  individual  organism. 

In  the  preceding  pages  I  have  endeavored  to  show 
what  causes  have  been  and  are  efficient  in  the  produc- 
tion of  different  types  of  organic  life,  through  the 
modifications  of  the  bathmic  energy.  We  will  now 
briefly  consider  the  question  of  the  origin  of  the  living 
substance,  protoplasm  or  sarcode,  which  exhibits  bath- 
mism. 

On  this  subject  Professor  Manly  Miles  remarks  :l 
"Omitting  subordinate  details,  which  represent  the 
separate  links  in  the  chain  of  events,  the  processes  of 
nutrition  may  be  summarized  in  general  terms  as  fol- 
lows :  In  plants  the  chemical  elements  and  binary  com- 
pound on  which  they  feed,  are  built  up  by  successive 
steps  of  increasing  complexity  and  instability  into  pro- 
toplasm, with  a  storing  of  the  energy  made  use  of  in 
the  constructive  process,  which  is  derived  from  the 
heat  and  light  of  the  sun.  The  constructive  processes 
are  expressed  by  the  term  anabolism,  and  the  products 
of  the  different  upward  steps  are  called  anastatic.  Pro- 
toplasm, the  most  complex  and  unstable  of  organic 
substances,  is  the  summit  of  the  ascending  steps  of 
anabolism  ;  and  katabolism,  which  represents  the  suc- 
ceeding downward  steps  of  metabolism,  then  follows, 
and  its  products  or  katastates  are  starch,  cellulose, 
proteids,  etc.,  or  what  we  recognize  as  the  proximate 

1  Proceeds.  Amer  Assoc.  Adi'.  Set.,  1892,  p.  203. 


482    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

constituents  and  tissues  of  plants."  I  interject  here 
the  remark,  that  from  a  chemical  point  of  view,  pro- 
toplasm is,  under  certain  conditions,  not  unstable. 

If  the  tendency  of  the  catagenetic  energies  is  away 
from  vital  phenomena,  it  is  impossible  that  they,  or 
any  of  them,  should  be  the  cause  of  the  origin  of  liv- 
ing matter.  This  logical  inference  is  confirmed  by  the 
failure  of  all  attempts  to  demonstrate  spontaneous  gen- 
eration of  living  organisms  from  inorganic  matter. 
Further,  the  principle  of  continuity  leads  us  to  infer 
that  the  energy  which  produced  organic  matter  must 
be  identical  with  or  allied  to  that  which  is  the  efficient 
agent  in  progressive  evolution  of  organisms,  and  is, 
therefore,  anagenetic.  Such  a  conclusion  may  seem 
to  lead  to  a  dualism  which  is  itself  opposed  to  the 
principle  of  continuity  or  uniformity,  and  which  is  op- 
posed to  experience  of  the  phenomena  of  energy  in 
general.  How  is  uniformity  to  be  harmonized  with 
the  hypothesis  of  two  types  of  energy  acting  in  differ- 
ent directions,  apparently  in  opposition  to  each  other? 
Since  facts  and  logic  do  not  support  the  derivation  of 
the  anagenetic  from  the  inorganic  energies,  can  the  re- 
verse process,  the  derivation  of  the  catagenetic  from 
the  anagenetic  be  and  have  been  the  order  of  nature? 
In  support  of  this  hypothesis,  we  have  the  universal 
prevalence  of  the  retrograde  metamorphosis  of  energy 
in  both  the  inorganic  and  organic  kingdoms.  Phe- 
nomena of  structural  degeneracy  are  well  known  in 
the  organic  world,  and  purely  chemical  phenomena  in 
both  organic  and  inorganic  processes  are  all  degenerate. 
It  appears,  then,  much  more  probable  that  catagenesis 
succeeds  anagenesis  as  a  consequence,  and  does  not 
precede  it  as  a  cause.  In  other  words,  it  is  more 


THE  ENER  G  Y  OF  E  VOL  UTION.  483 

probable  that  death  is  a  consequence  of  life,  rather  than 
that  the  living  is  a  product  of  the  non-living.  I  have 
therefore  given  to  that  energy  which  is  displayed  by 
the  plant  in  the  elaboration  of  living  from  non-living 
matter  the  name  of  antichemism.1  Thus,  while  the 
heat  of  the  sun  is  necessary  to  the  building  of  proto- 
plasm, within  a  certain  range  of  temperature  this  form 
of  energy  has  its  opportunity. 

The  actual  demonstration  of  this  hypothesis  can 
only  come  from  researches  into  the  thermochemistry 
of  proteids  and  protoplasm.  As  these  substances  have 
not  been  made  in  the  laboratory,  these  researches  are 
not  yet  possible.  We  may,  however,  consider  the 
problem  as  follows.  In  the  process  of  making  pro- 
toplasm, three  gases,  oxygen,  hydrogen,  and  nitrogen 
are  converted  into  a  semisolid.  In  this  case  heat 
should  be  dissipated,  to  an  amount  reduced  by  the 
molecular  dissolution  of  carbon.  This  is  however 
not  the  case,  for  heat  is  absorbed  with  an  integration 
of  atomic  bonds.  In  other  words,  it  would  seem  that 
the  manufacture  of  protoplasm  by  plants  is  an  endo- 
thermic  process.  This  view  is  strengthened  by  the  dis- 
covery by  Berthollet2  that  the  production  of  numerous 
solid  organic  substances,  in  which  organic  bases  are 
used,  is  also  endothermic.  These  facts  confirm  the  in- 
ference above  recited,  that  the  phenomena  of  organic 
growth  involve  the  absorption  of  energy  and  not  its 
dissipation. 

Referring  to  the  composition  of  protoplasm  C OH 
IV,  I  have  called  attention  to  the  fact  that  each  of  its 
elements  represents  one  of  the  great  divisions  defined 

^American  Naturalist,  1884,  p.  979;    Origin  of  the  Fittest,  1887,  p,  431. 
ZAnnales  de  Chimie  et  de  Physique,  VI,  1895,  p.  232. 


484   PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

by  their  valency,  into  which  the  ultimate  substances 
of  nature  naturally  fall.  This  combination  I  have  sug- 
gested might  account  for  the  chemical  inertness  of 
protoplasm,  through  the  mutual  inhibition  which  each 
of  these  elements  might  be  supposed  to  exercise  over 
the  other,  owing  to  the  diversity  of  their  modes  of 
chemical  action. 

In  order  to  present  more  clearly  the  views  enun- 
ciated in  the  preceding  pages,  I  give  a  synoptic  table 
of  energies. 


I.  Anagenetic 


II.  Catagenetic 


f   Antichemism 

Organic                       j   Bathmism 

Exclusively                  f   Neurism 

organic                     \   Myism 

Radiant  Energy 

Inorganic  and 

Chemism 

Cohesion 

organic 

Gravitation 

2.  BATHMOGENESIS. 

The  innumerable  structures  which  are  due  to  the 
activity  of  bathmisms  may  be  supposed  to  result  from 
the  composition  of  the  inherited  form  with  energies 
which  are  derived  from  sources  external  to  the  germ- 
plasma,  whether  within  the  soma  or  external  to  it. 
These  interferences  produce  new  and  specific  types  of 
energy.  The  inherited  bathmism  I  have  termed  "sim- 
ple growth  force, "  and  the  modified  forms  I  have  termed 
'  <  grade  growth  force. " l  It  appears  that  these  types  of 
energy  should  be  distinguished  by  special  names. 
Hence  I  have  proposed  to  restrict  the  term  bathmism 

"^Proceedings  American  Philosophical  Society,  1871,  p.  253. 


THE  EN  ERG  Y  OF  E  VOL  UTION.  485 

to  the  modified  or  "grade"  growth  force,  and  to  term 
the  inherited  or  "simple"  type  of  growth  force,  em- 
phytism.1  As  a  matter  of  fact,  pure  emphytism  can 
only  be  observed  in  the  embryos  of  sexless  or  parthe- 
nogenetic  origin,  and  in  the  repair  of  tissues. 

Ryder  has  called  the  exhibition  of  growth-energy 
ergogenesis,  and  he  calls  attention  to  the  fact  that  it 
appears  under  two  aspects.  In  the  first,  ergogenesis 
is  due  to  mechanical  causes  resident  in  the  organism 
exclusively,  and  consists  of  the  physical  tensions  in- 
herent in  protoplasm  under  all  the  conditions  of 
growth.  With  these  the  growth-energies  have  to 
reckon,  as  they  are  the  conditions  which  underlie  them. 
They  are  not,  .however,  strictly  speaking,  growth- 
energies,  but  would  be  exhibited  by  any  similar  col- 
loid under  similar  conditions.  To  the  movements  due 
to  physical  causes  under  these  circumstances,  Ryder 
gives  the  name  of  Statogenesis.2  The  second  aspect 
of  the  energies  necessary  to  growth  is  present  under 
the  two  forms  already  referred  to,  as  emphytism  and 
bathmism.  The  latter  class,  or  interference  energies, 
are  naturally  differentiated  into  those  which  are  due 
to  physical  (or  chemical)  external  agencies  (molecular 
movements),  and  those  that  are  due  to  molar  move- 
ments as  expressed  in  tissues,  as  impact,  strain,  etc. 
To  the  former  I  have  given  the  name  of  physiobath- 
mism,  to  the  latter,  kinetobathmism.3 

The  relations  of  these  forms  of  energy  may  be  rep- 
resented in  tabular  form  as  follows : 


II  have  supposed  in  a  late  paper  (American  Naturalist,  1894,  p.  212)  that 
this  is  the  statogenic  energy  of  Ryder.  This  mistake  has  been  corrected. 

2 Proceedings  American  Philosophical  Society,  1893,  p.  194. 

^American  Naturalist,  1894,  p.  214.  The  two  types  of  growth  are  then 
physiogenesis  and  kinetogenesis.  (Origin  of  the  Fittest,  1887,  p.  423.) 


486    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

Ergogenesis 
Catagenetic       Statogenesis 

f  Inherited     Emphytogenesis 
Anagenetic    \  With  inter-  Molecular 


I      ference      Bathmogenesis 


Phy  Biogenesis 


Molar     Kinetogenesis 

Emphytogenesis  I  shall  hereafter  endeavor  to  show 
is  an  automatic  (catagenetic)  product  of  bathmogen- 
esis,  and  a  stationary  factor  in  evolution. 

The  above  table  is  designed  to  be  a  classification 
and  formulation  of  the  innumerable  well-known  facts 
of  organic  growth  and  evolution.  It  does  not  pre- 
tend to  be  an  explanation  of  the  processes  involved, 
but  it  is  the  first  step  to  be  taken  in  attempting  the 
explanation,  i.  e.  a  discrimination  and  classification  of 
its  factors. 

Ryder  thus  expressed  the  relation  between  stato- 
genesis  and  kinetogenesis.1 

"So  universal  is  this  interference  of  the  statical 
conditions  of  the  plasma  of  segmenting  ova  with  the 
ontogenetic  processes,  that  not  a  single  metazoan  or- 
ganism can  be  named,  the  development  of  which  is  not 
thus  marred  in  some  way  or  other.  It  is  often  a  long 
time  relatively  after  development  has  begun  that  there 
is  any  obvious  delineation  of  the  embryo.  In  fact, 
this  cannot  take  place  until  the  statical  energies  of 
surface-tension  which  have  kept  the  egg  globular  are 
overridden.  In  so  far  as  the  ontogeny  of  any  organ- 
ism is  marred  by  statical  conditions  of  energy- display, 
its  embryonic  form  is  also  modified.  In  so  far  as  such 
statical  interference  affects  the  figure  of  the  organism 
they  are  morphogenetic  or  form-determining.  In  so 
far  the  figure  of  a  developing  being  is  disturbed  or 

^•Proceeds.  Amer.  Philos.  Society,  1893,  pp.  197-201. 


THE  ENERGY  OF  EVOLUTION.  487 

modified  by  statical  agencies  its  figure  may  be  said  to 
be  subject  to  statogenetic  influences.  No  existing 
larval  form  has  escaped  the  influence  upon  its  own 
shape  of  a  constantly  active  statical  equilibrium  of  its 
own  substance.  There  is,  therefore,  a  constant  strug- 
gle going  on  during  development  between  the  phylo- 
genetic  and  ontogenetic  forces,  determining  the  se- 
quence and  relations  of  the  successive  cleavages  of  the 
egg  and  the  statical  equilibria  that  obtain  amongst  its 
several  parts.  Statogenetic  processes  are,  therefore,  as 
constant  and  universal  as  the  phylogenetic  and  onto- 
genetic. One  may  even  go  so  far  as  to  say  that  possi- 
bly the  relations  thus  tending  to  be  established  by 
statical  conditions  may  tend  to  become  transmissible 
as  hereditary  tendencies.  Such  indeed  is  the  view  up- 
held by  Prof.  E.  B.  Wilson  in  his  remarkable  paper  on 
'  The  Cell-Lineage  of  Nereis. '  I  have  myself  seen  no 
less  than  three  consecutive  recurrences  of  the  same 
statical  conditions  in  a  fish  egg,  none  of  which  can, 
for  this  reason,  be  definitely  proved  to  be  purely  onto- 
genetic. 

"While  such  phenomena  as  those  of  the  genesis 
of  the  heterocercal  or  upwardly  deflected  condition  of 
the  axis  in  the  tails  of  fishes,  or  the  downwardly  de- 
flected condition  of  the  axis  in  Ichthyosauri  are  almost 
purely  kinetogenetic,  the  multiplicity  of  factors  con- 
cerned, statogenetic  as  well  as  ontogenetic  and  phylo- 
genetic, must  always  be  considered  and  each  given  its 
due  weight  and  importance  in  achieving  the  morpho- 
genetic  result.  That  there  is  an  absolute  conflict  be- 
tween statogeny  and  kinetogeny  on  the  one  hand,  and 
of  phylogeny  and  ontogeny  on  the  other,  in  the  case 
of  the  development  of  the  ova  of  multicellular  forms 
admits  of  no  doubt.  All  metazoa  pass  through  larval 


488    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

stages  in  which  the  statical  conditions  of  equilibrium 
of  the  plasma  of  the  egg  is  gradually,  in  a  great  meas- 
ure, overriden  by  the  hereditary  energies  represented 
by  phylogeny  and  ontogeny.  That  there  still  remain 
traces  of  the  effects  of  kinetogeny  and  statogeny  in  the 
adult  organism  cannot  be  denied  in  view  of  the  facts 
to  be  derived  from  the  shapes  of  tissue  elements,  and 
even  of  organs,  as  the  foregoing  paragraphs  show." 

The  first  appearance  of  bathmogenetic  action  is  the 
first  modification  of  the  statogenetic  and  emphytogen- 
etic  energies  from  whatever  source.  Changes  may  be 
effected  in  the  weight,  color,  and  in  functional  capacity 
by  temperature,  humidity,  food,  etc.,  thus  exhibiting 
physiogenesis.  Or  changes  in  the  size  and  forms  of 
parts  of  the  body  may  be  produced  by  movements  of 
the  organism,  or  of  its  environment,  so  displaying  ki- 
netogenesis.  So  long  as  these  modifications  of  struc- 
ture should  be  confined  to  the  individuals  thus  modi- 
fied, there  would  be  no  evolution.  A  second  genera- 
tion, if  not  subjected  to  the  same  stimuli,  would  not 
possess  the  modifications ;  and  their  possession  of  them 
would  depend  entirely  on  the  amount  of  stimulus.  In 
other  words,  there  would  be  no  accumulation  of  modi- 
fication. It  has,  however,  been  generally  believed  that 
these  modifications  are  inherited,  and  I  think  it  has 
been  shown  that  this  belief  rests  on  a  solid  basis.  Mean- 
while I  have  called  the  bathmogenesis  which  does  not 
extend  beyond  the  generation  in  which  it  appears, 
autobathmogeny. 

The  quantitative  relation  which  necessarily  exists 
between  bathmism  and  its  sources  may  be  expressed 
as  follows,  with  due  recognition  of  the  fact  that  such 
expression  does  not  rest  upon  any  experimental  tests. 
Emphytogenesis  is  work  done  in  the  construction  of 


THE  ENERG  Y  OF  E  VOL  UTION.  489 

tissues  like  those  of  the  parent  and  without  interfer- 
ence. Here  we  have  the  molecular  energy  of  the  par- 
ent converted  into  the  molar  movements  observed  to 
be  concomitants  of  segmentation  ;  to  be  represented 
in  the  completed  tissue  by  the  mutual  tensions  by  vir- 
tue of  which  each  structural  element  maintains  its  in- 
tegrity. It  is  evidently  a  process  of  metamorphosis  of 
energy  in  which  there  is  less  waste  than  in  any  other 
known  to  us.  Embryonic  growth  is  accompanied  by 
a  very  slight  dissipation  of  heat,  since  a  slight  rise 
of  temperature  is  noticeable  in  the  eggs  of  cold-blooded 
animals  and  in  flowers,  when  reproduction  is  active. 
The  products  of  breaking  down  are  equally  rare  in 
embryonic  growth,  and  both  this  and  the  dissipation 
of  heat  are  perhaps  largely  due  to  the  changes  wrought 
in  non-cleavable  nutritive  substances  with  which  the 
yolks  are  sometimes  charged.  It  is  probably  to  ac- 
complish this  process  that  the  oxygen  necessary  for  the 
embryonic  growth  is  used.  How  much  loss  is  due  to 
cell-division  itself  is  not  known,  but  it  must  be  very 
little  if  any.  We  have  probably  here  a  nearly  perfect 
conversion  of  energy.  Theoretically  we  have  ana- 
genesis wherever  the  up-building  exceeds  the  down- 
breaking. 

The  attempt  to  realize  in  the  imagination  the 
modus  operandi  of  bathmic  energy  in  embryo-building 
takes  the  following  form.  It  is  to  be  supposed  that 
movement  which  has  been  most  frequently  repeated, 
and  for  the  longest  period,  is  prepotent,  and  takes 
precedence  of  all  others.  This  is  clearly  simple  cell- 
division,  which  follows  the  nutrition  supplied  by  the 
spermatozoon,  and  which  represents  the  first  act  of 
animal  life.  Hence,  segmentation  of  the  oosperm  is 
the  first  movement  of  bathmism.  Each  subsequent 


4QO    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

movement  appears  in  the  order  of  potency,  which  is, 
other  things  being  equal,  a  time  order,  or  the  order  of 
record.  The  cause  of  the  localization  of  tissues  and 
structures  is  much  more  difficult  to  understand  than 
the  cause  of  the  order  of  their  appearance.  The  more 
energetic  part  of  the  process  naturally  requires  the 
greater  space  for  its  products.  The  ectoderm,  which 
becomes  the  seat  of  the  nervous  axis  and  its  muscular 
adjuncts,  occupies  the  superficial  portions  of  the  yolk. 
Hence,  we  may  regard  this  expression  of  the  struc- 
tural record  of  these  functions  as  more  energetic  than 
that  of  the  record-structure  of  the  nutritive  functions, 
which  displays  itself  below  the  ectoderm.  In  mero- 
blastic  and  amphiblastic  embryos,  the  segmentation 
which  develops  the  nutritive  tissues  is  evidently  more 
sluggish,  for  the  cells  are  larger  and  fewer  in  number, 
than  those  of  the  ectoderm. 

In  evolution  external  stimuli  modify  the  course  of 
emphytogeny  above  described,  and  by  producing  new 
structural  records,  cause  a  new  form  of  energy,  due  to 
composition  of  the  new  with  the  old,  and  the  process 
of  growth  then  becomes  bathmogeny.  The  external 
stimuli  are  molecular  or  molar,  determining  physio- 
bathmism  or  kinetobathmism. 

The  effect  of  motion  or  use  on  the  soma  may  be 
conveniently  termed  autokinetogenesis.  Moderate  use 
of  a  muscle  is  known  to  increase  its  size.  Irritation 
of  the  periosteum  is  known  to  cause  deposit  of  bone. 
Friction  and  pressure  of  the  epithelium  increases  its 
quantity  or  changes  its  form.  Increased  activity  of 
the  functions  of  nervous  tissues  increases  their  relative 
proportions,  as  in  the  enlargement  of  nerves  which  re- 
place others  which  are  interrupted  by  mutilations,  etc. 


THE  ENERGY  OF  EVOLUTION.  491 

On  the  other  hand,  it  is  equally  well  known  that  disuse 
produces  diminution  of  muscular  tissues,  and  through 
it,  a  reduction  in  the  quantity  of  the  harder  tissue 
(bone,  chitin,  etc.)  to  which  it  is  attached  (as  muscu- 
lar insertions,  etc.).  It  was  the  observation  of  such 
well-known  phenomena  as  these  that  led  Lamarck  to 
advance  his  doctrine  of  evolution  under  use  and  dis- 
use, and  which  has  led  many  others  to  give  their  ad- 
herence to  such  a  view. 

Thus  much  for  cell-growth.  Another  class  of  mod- 
ifications of  a  similar  kind  may  be  found  in  the  parts 
of  an  organism  which  consist  of  a  complex  of  cells,  or 
tissues.  Thus  the  lumen  of  a  small  artery  is  enlarged 
under  the  influence  of  pressure  when  it  is  compelled 
to  assume  the  function  of  a  larger  vessel  through  the 
interruption  of  the  latter.  A  part  of  an  internal  or 
external  skeleton  which  is  fractured  will  form  an  arti- 
ficial joint  at  the  point  of  fracture,  if  the  adjacent  sur- 
faces are  kept  in  motion.  Marey  (Animal  Mechanism, 
pp.  88-89)  says,  "After  dislocations  the  old  articular 
cavities  will  be  filled  up  and  disappear,  while  at  the 
new  point  where  the  head  of  the  bone  is  actually  placed, 
a  fresh  articulation  is  formed,  to  which  nothing  will  be 
wanting  in  the  course  of  a  few  months,  neither  articu- 
lar cartilages,  synovial  fluid,  nor  the  ligaments  to  re- 
tain the  bone  in  place."  I  have  given  some  illustra- 
tions of  this  fact,1  which  have  come  under  my  observa- 
tion, and  which  have  an  important  bearing  on  the 
origin  of  the  articulations  of  the  vertebrate  skeleton  as 
I  have  traced  them  throughout  geological  time.  I 
have,  as  I  think,  conclusively  shown  that  these  varied 
structures  have  been  produced  by  impacts  and  strains, 

IPage  275  and  Proceeds,  Atner.  Philos.  Soc.t  1892,  p.  285. 


492    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

which  are  concomitants  of  the  movements  of  the  ani- 
mals, acting  through  long  periods  of  time.1 

The  term  mnemogenesis  is  employed  by  Professor 
Hyatt2  to  characterize  the  manner  in  which  kinetogen- 
esis  is  supposed  to  produce  results  in  inheritance.  I 
have  suggested  that  the  phenomena  of  recapitulation, 
characteristic  of  ontogeny  (American  Naturalist,  Dec., 
1889),  are  due  to  the  presence  of  a  record  in  the  germ 
cells,  having  a  molecular  basis  similar  to  that  of  mem- 
ory. This  view  is  adopted  by  Professor  Hyatt.  I  have 
already  referred  to  it  in  the  preceding  pages. 

A  general  statement  of  this  doctrine  was  made  by 
Mr.  Sedgwick  in  The  British  and  Foreign  Medico- Chir- 
urgical  Review  for  July  1863  in  the  following  language  : 
"For  atavism  in  disease  appears  to  be  but  an  instance 
of  memory  in  reproduction,  as  imitation  is  expressed 
in  direct  descent ;  and  in  the  same  way  that  memory 
never,  as  it  were,  dies  out,  but  in  some  state  always 
exists,  so  the  previous  existence  of  some  peculiarity  in 
organization  may  likewise  be  regarded  as  never  abso- 
lutely lost  in  succeeding  generations,  except  by  ex- 
tinction of  race."  The  next  formulation  of  mnemo- 
genesis is  by  Hering  in  1870. 3 

It  is  concentrated  in  the  following  paragraph  : 

"The  appearance  of  properties  of  the  parental  or- 
ganism in  the  full-grown  filial  organism  can  be  noth- 
ing else  but  the  reproduction  of  such  processes  of 
organized  matter  as  the  germ  when  still  in  the  germi- 
nal vesicles  had  taken  part  in  ;  the  filial  organism  re- 
members, so  to  speak,  those  processes,  and  as  soon  as 

1"  Mechanical  Origin  of  the  Hard  Parts  of  the  Mammalia,"  Amer.  Journal 
of  Morphology,  1889.     Origin  of  the  Fittest,  1887,  pp.  305-373. 

2  Proceeds.  Boston  Soc.  Nat.  History,  1893,  p.  73. 

3  Address  before  the  Imperial  Academy  of  Sciences  of  Vienna,    May  30, 
1870,  by  Ewald  Hering;  English  translation,  Chicago,  1895. 


THE  ENERGY  OF  EVOLUTION,  493 

an  occasion  of  the  same  or  similar  irritations  is  offered, 
a  reaction  takes  place  as  formerly  in  the  parental  or- 
ganism, of  which  it  was  then  a  part  and  whose  desti- 
nies influenced  it."  In  explanation  of  this  theory, 
Hering  says  :  "We  notice,  further  on,  that  the  process 
of  development  of  the  germs  which  are  destined  to 
attain  an  independent  existence,  exercises  a  powerful 
reaction  both  on  the  conscious  and  unconscious  life  of 
the  whole  organism.  And  this  is  a  hint  that  the  organ  of 
germination  is  in  closer  and  more  momentous  relation 
to  the  other  parts,  especially  to  the  nervous  system, 
than  any  other  organ.  In  an  inverse  ratio,  the  conscious 
destinies  of  the  whole  organism,  it  is  most  probable, 
find  a  stronger  echo  in  the  germinal  vesicles  than  else- 
where. " 

If  heredity  is  a  form  of  memory,  its  laws  may  re- 
semble those  of  the  psychic  memory.  In  the  latter, 
everything  depends  on  what  we  call  the  strength  of 
the  impression.  A  single  impression  is  often  easily 
forgotten,  and  the  certainty  of  recollection  is  largely 
dependent  on  the  frequency  of  repetition  of  the  stimu- 
lus. This  is  the  essence  of  mental  education,  and  it 
is  probably  the  law  of  education  of  the  germ-plasma 
as  well.  Thus  may  be  understood  how  stimuli  end- 
lessly repeated  through  long  geologic  ages,  must  pro- 
duce results  far  more  profound  and  lasting  than  spo- 
radic impressions  of  modern  and  artificial  origin. 

It  must  be  here  remarked  for  the  benefit  of  the 
reader  who  may  be  unfamiliar  with  the  explanation  of 
the  psychic  memory,  that  it  is  the  conscious  part  of 
memory  which  gives  it  its  psychic  character.  This 
side  is  due  to  a  fundamental  molecular  arrangement 
caused  by  stimuli,  which  may  be  retained  for  long 
periods  without  expression  in  consciousness.  Thus 


494    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

Bain  regards  memory  as  consisting  of  an  unconscious 
and  a  conscious  stage,  and  the  latter  he  terms  rem- 
iniscence. Other  psychologists  in  common  with  man- 
kind generally,  use  the  word  memory  for  the  conscious 
expression.  I  have  termed  the  unconscious  condition 
of  the  molecular  basis  of  mind,  cryptopnoy. 


CHAPTER  X.— THE  FUNCTION  OF 
CONSCIOUSNESS. 


i.  CONSCIOUSNESS  AND  AUTOMATISM. 

/CONSCIOUSNESS  is  a  general  term,  which  em- 
v_y  braces  all  forms  of  self-knowledge.  Sentiency  is 
sometimes  used  with  an  identical  meaning.  Conscious- 
ness must  be  distinguished  from  self-consciousness, 
which  implies  introspection.  Consciousness  may  or 
may  not  be  characterised  by  attention.  There  are  two 
widely  different  types  of  consciousness,  viz.,  the  pre- 
sentative  and  the  representative.  The  former  includes 
sense-perception  only;  the  latter  includes  all  the  com- 
binations of  sense-perception  which  characterize  men- 
tal action,  from  simple  memory  to  the  most  compre- 
hensive classification  and  conception.  Most,  if  not 
all,  animals  appear  to  possess  sense-perception,  and 
all  such  possess  the  representative  faculty  of  memory; 
but  the  higher  grades  of  representative  mental  function 
are  not  so  general  among  animals,  and  the  extent  of 
their  occurrence  is  yet  in  dispute. 

In  the  preceding  pages  I  have  endeavored  to  show 
that  the  factors  of  evolution  are  bathmogenesis  cor- 
rected by  natural  selection.  Bathmogenesis  embraces 
the  two  factors  physiogenesis  and  kinetogenesis,  or  the 
products  of  molecular  and  molar  motion,  respectively. 


4g6    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

These  two  forms  of  motion  have  been  coextensive 
with  the  existence  of  life,  neither  one  preceding  the 
other  in  time.  Statogenesis  is  the  expression  of  a  form 
of  energy  which  characterizes  inorganic  matter,  while 
bathmogenesis  is  entirely  peculiar  to  living  things. 
Kinetogenesis  is  the  fundamental  principle  in  organic 
evolution,  since  "it  determines  the  amount  and  kind 
of  physiogenesis,  because  it  creates  the  environment 
which  furnishes  the  conditions  of  physiogenesis.  Pro- 
gressive organic  evolution  may,  then,  be  described  as 
due  to  kinetogenesis  corrected  by  natural  selection. 
At  the  basis,  however,  molar  organic  motion,  i.  e.,  con- 
traction of  protoplasm,  is  probably  molecular,  but  it  is 
distinguished  from  other  forms  of  molecular  motion  in 
the  vast  aggregate  of  molecules  which  move  simultan- 
eously in  one  direction,  as  in  an  amreba  or  a  muscle, 
thus  effecting  a  change  in  the  position  of  all  or  a  part 
of  an  organism.  Hence  the  distinction  is  a  real  one. 
Molar  motion  being,  then,  of  such  fundamental  im- 
portance as  a  factor  in  evolution,  the  cause  of  such 
motion  is  also  a  capital  question.  Contraction  of 
protoplasm  is  caused  by  stimuli,,  such  as  currents  of 
electricity  and  chemical  reagents ;  but  such  stimuli  are 
not  those  which  ordinarily  produce  the  contractions  to 
which  the  molar  movements  of  living  animals  are  due. 
In  those  animals  which  possess  a  nervous  system  it 
has  been  shown  that  contractions  only  follow  stimuli 
which  are  conveyed  to  the  contractile  elements  by 
nervous  threads,  and  the  internal  energy  which  repre- 
sents the  external  stimulus,  is  called  nervous  energy 
or  neurism.  In  animals  without  a  nervous  system,  and 
in  plants,  external  stimuli  must  be  justly  supposed  to 
be  converted  into  the  same  form  of  energy,  which  in 
such  organisms  has  a  general  circulation  throughout 


THE  FUNCTION  OF  CONSCIOUSNESS.  497 

the  contractile  protoplasm.  The  important  point  about 
these  movements  in  most  animals  is,  that  their  direc- 
tion directly  subserves  the  attainment  of  some  position 
which  is  favorable  for  the  procurement  of  relief  from 
some  unpleasant  sensation,  or  the  acquisition  of  some 
agreeable  one,  or  both.  We  have  the  best  reasons  for 
believing  this  to  be  true  of  the  vast  majority  of  animals, 
because  their  structure  is  fundamentally  like  our  own, 
and  the  inference  that  the  same  is  true  of  the  lowest 
forms  of  life  is  justifiable  until  it  is  proven  to  be  mis 
taken. 

Lamarck  has  attributed  the  movements  of  animals 
to  the  necessity  of  satisfying  their  instincts,  without 
entering  into  the  metaphysical  questions  which  this 
involves.  I  have  regarded  the  question  as  a  meta- 
physical one  by  asserting  that  the  necessary  prelim- 
inary to  movement  is  "effort,"  referring  to  what  are 
called  "voluntary"  as  distinguished  from  automatic 
motions.1 

Without  special  organs  of  movement,  a  great  part  of 
the  phenomena  of  kinetogenesis  would  have  no  exis- 
tence, precisely  as  natural  selection  cannot  act  unless 
the  materials  for  selection  (i.  e.  variations)  are  already 
in  existence.  In  explanation  of  the  origin  of  organs 
of  movement  we  have  the  general  ability  of  the  primi- 
tive animal,  or  protozoon,  to  project  portions  of  its 
body-substance  as  pseudopodia,  which,  in  more  spe- 
cialized forms,  become  persistent  and  more  or  less 
rigid,  as  flagella,  cilia,  etc. ;  which  are  the  first  distinct 
organs  which  subserve  the  transportation  of  the  body 
from  place  to  place.  The  causes  which  lead  to  these 
changes  are  as  yet  obscure,  but  that  the  use  of  these 

1  Proceeds.  Am.  Philos.  Soc.,  1871,  p.  18.  Origin  of  the  Fittest,  1887,  p.  194. 
390 


498    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

organs  when  once  called  into  existence  is  due  to  stimuli 
similar  to  those  which  affect  the  motions  of  the  limbs 
of  the  higher  animals,  is  altogether  probable.  What- 
ever be  its  nature,  the  preliminary  to  any  animal  move- 
ment which  is  not  automatic,  is  an  effort.  And  as  no 
adaptive  movement  is  automatic  the  first  time  it  is  per- 
formed, we  may  regard  effort  as  the  immediate  source 
of  all  movement.  Now,  effort  is  a  conscious  state,  and 
is  a  sense  of  resistance  to  be  overcome.  When  an  act 
is  performed  without  effort,  resistance  has  been  over- 
come, and  the  mechanism  necessary  for  the  performance 
of  the  act  has  been  completed.  The  stage  of  automa- 
tism has  been  reached.  At  the  inception  of  a  new 
movement  resistance  is  necessarily  experienced.  It  is 
generally  believed  that  a  mental  state,  as  a  sensation 
or  a  desire,  which  may  or  may  not  stimulate  a  rational 
process  as  an  intervening  element  in  the  circuit,  is 
concerned  in  overcoming  this  resistance. 

A  different  view  is  held  by  certain  physiologists  and 
metaphysicians,  as  e.  g.  Wundt  and  Hoffding.  Hux- 
ley thus  states  his  opinion  in  his  Belfast  address  of 
ity^b  propos  of  Descartes's  doctrine  that  all  animals 
below  man  are  automata.  "The  consciousness  of 
brutes  would  appear  to  be  related  to  the  mechanism  of 
their  body  simply  as  a  collateral  product  of  its  work- 
ing, and  to  be  as  completely  without  any  power  of 
modifying  that  working  as  the  steam-whistle  which 
accompanies  the  work  of  a  locomotive-engine  is  with- 
out influence  on  its  machinery.  Their  volition,  if  they 
have  any,  is  an  emotion  indicative  of  physical  changes,  not 
a  cause  of  such  changes."  (Italics  mine.)  In  other 
words,  stimulus  excites  conscious  states,  but  the  state 
thus  produced  has  no  influence  on  the  resulting  act. 

^Scientific  Culture  and  Other  Essays,  p.  243. 


THE  FUNCTION  OF  CONSCIOUSNESS.  499 

That  sense-perceptions  are  stimuli  to  the  immediate 
appearance  of  structural  changes  or  movements  is  ad- 
mitted. This  is  shown  by  the  production  of  color 
changes  in  animals  through  changes  in  the  condition 
of  the  organs  of  sight.  Pouchet  showed  that  the  extir- 
pation of  both  eyes  of  the  turbot,  and  of  a  Gobius, 
paralyzed  the  chromatophorous  cells,  so  that  the  usual 
color-adaptations  to  the  color  of  the  surface  of  the  bot- 
tom on  which  they  rested,  could  not  be  made.  He  also 
produced  the  same  effect  on  one  side  of  a  trout  by  re- 
moving the  eye  of  the  opposite  side.  The  chromato- 
phorae  were  permanently  expanded,  and  the  colors  dark. 

Some  experiments  which  I  tried  with  tree  frogs  of 
the  species  Hyla  gratiosa,  and  Hyla  carolinensisy  are  as 
follows  :  The  color  is  usually  green  in  both  species, 
but  it  changes  to  dark  brown  where  the  frog  rests  on  a 
brown  surface,  as  of  bark,  etc.  It  appears  that  the 
maintenance  of  the  brown  color  requires  a  more  vigor- 
ous nervous  stimulus  than  the  green.  The  frogs  are 
green  at  death  ;  and  limbs  which  I  ligated  remained 
green  when  the  remainder  of  the  surface  became 
brown.  Now  in  individuals  with  extirpated  eyes,  the 
color  was  always  green,  no  matter  what  the  surface  on 
which  they  rested.  The  power  of  assuming  the  brown 
color  was  lost. 

In  these  experiments  it  is  difficult  to  connect  the 
expansion  of  the  chromatophorous  cells  as  any  effect 
of  consciousness  of  color,  by  direct  proof.  If,  how- 
ever, muscular  cells  can  be  contracted  under  the  in- 
fluence of  mental  states,  a  similar  mechanism  may  be 
supposed  to  exist  in  the  case  of  chromatophorae.  The 
fact  that  the  process  may  be  now  reflex  does  not  ex- 
clude the  other  fact  of  the  influence  of  consciousness 


500    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

at  the  inception,  and  its  necessity  for  the  continuance 
of  the  habit. 

If  we  examine  muscular  movements,  the  evidence 
of  control  by  consciousness  becomes  more  distinct. 
New  conditions  bring  forth  new  acts  in  animals  too 
frequently  to  permit  us  to  believe  otherwise.  Thus 
Mr.  Belt  tells  of  a  procession  of  ants  which  crossed  a 
railroad  in  Panama.  Many  were  killed  on  the  rail,  so 
the  column  excavated  a  passage  beneath  the  rail,  and 
thus  escaped  further  injury.  No  one  can  reasonably 
deny  the  intervention  of  a  conscious  state  of  a  hi'gh 
order,  as  directly  controlling  the  muscular  movements 
of  those  ants.  According  to  Beauchamp,  termites  in 
the  same  region  display  similar  intelligence.  A  num- 
ber of  them  were  confined  in  a  deep  glass  vessel  with 
smooth  sides  which  they  could  not  scale.  They  there- 
upon deposited  drops  of  their  building  secretion,  which 
hardens  on  drying,  on  the  glass,  ascending  backwards, 
and  so  made  a  stair  out  of  their  prison,  by  which  they 
escaped. 

A  Cebus  capucinus  in  my  possession  imitated  some 
carpenters  who  were  working  in  the  room  with  a  draw- 
ing-knife. He  used  a  triangular  piece  of  tin,  and, 
holding  the  corners,  drew  the  edge  towards  him  over 
the  surface  of  a  piece  of  squared  wood  on  which  he 
sat.  He  did  this  rapidly  and  repeatedly,  with  many 
grimaces.  A  Cebus  apella  in  the  Philadelphia  Zoologi- 
cal Garden  lights  matches  whenever  he  can  get  them. 
He  always  selects  the  proper  end,  and  holds  it  at  a 
proper  distance,  so  that  the  stick  is  not  broken  and  his 
fingers  are  not  burned.  He  strikes  them  on  the  rough 
outside  of  his  drinking-kettle.  My  Cebus  came  direct 
from  the  forests  of  Venezuela,  and  he  had  not  been 
educated  among  carpenters.  The  history  of  the  apella 


THE  FUNCTION  OF  CONSCIOUSNESS.  501 

I  do  not  know,  but  he  had  not  probably  been  brought 
up  among  matches,  and  his  act  was  in  any  case  not 
reflex. 

As  an  illustration  of  the  simplest  of  movements, 
and  their  physical  conditions,  I  cite  those  of  the  Myx- 
omycetes,  from  Stahl.1 

' 'The  movement  of  Myxomycetes  is  influenced  by: 

"i.  Moisture  (Hydro tropism) :  In  their  young 
stages  they  wander  from  the  parts  of  the  substratum 
(i.  e.  of  the  deposit  on  which  they  are  creeping),  which 
are  gradually  drying  up,  toward  those  which  continue 
moist  longer  ;  '  it  is  even  possible,  by  bringing  moist 
bodies  into  the  proximity  of  any  ramifications,  to  cause 
the  production  of  pseudopodia,  which  elevate  them- 
selves from  the  substratum,  and  soon  come  into  con- 
tact with  the  moist  object,  so  as  to  enable  the  whole 
mass  of  the  plasmodium  to  migrate  on  to  it.'  On  the 
entrance  of  the  plasmodia  into  the  fructifying  condi- 
tion, positive  hydrotropism  gives  place  to  negative  ; 
the  myxomycete  quits  the  moist  substratum  and  creeps 
upwards  on  to  the  surface  of  dry  objects. 

"2.  Unequal  distribution  of  warmth  in  the  sub- 
stratum, and 

"3.  Unequal  supplies  of  oxygen  also  cause  loco- 
motion in  the  myxomycete. 

"4.  Chemical  substances  soluble  in  water  have  a 
similar  action.  Contact  of  the  plasmodia  on  one  side 
with  solutions  of  common  salt,  saltpetre,  or  carbonate 
of  potash,  cause  them  to  withdraw  from  the  danger- 
ous spot,  while  infusion  of  tan,  or  a  dilute  solution 
of  sugar,  produces  a  flow  of  the  protoplasm  and  ulti- 


1E.  Stahl,  "Zur  Biologie  der  Myxomyceten,"  Botan.  Zeitung,  1884,  No. 
10-12.  Abstract  in  Sitzungsbericht  der  Jenaischen  Gesellschaft  fur  Medizin 
und  Naturw issenschaft,  1883,  Sitzung  vom  16.  November. 


502    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

mately  translocation  of  the  whole  plasmodial  mass 
towards  the  source  of  nourishment.  Some  solutions 
have  an  attractive  or  repulsive  effect,  according  to 
their  degree  af  concentration. 

"5.  Finally,  they  withdraw  from  light  (negative 
heliotropism). 

"With  regard  to  the  acceleration  or  definite  direc- 
tion of  movement  produced  entirely  by  stimuli,  com- 
pare the  following : 

"The  knowledge  of  the  remarkably  delicate  reac- 
tion of  the  plasmodia  under  external  influences  enables 
us  to  comprehend  how  these  tender  structures,  desti- 
tute of  every  kind  of  external  protection,  are  able  to 
carry  on  their  existence.  The  plasmodia  which  are 
not  yet  ripe  for  reproduction  are  kept  in  the  moist  sub- 
stratum by  positive  hydrotrppism,  which  is  assisted  by 
negative  heliotropism. 

"But  within  the  darkness  and  moisture  of  the  sub- 
stratum the  plasmodia  by  no  means  remain  in  one 
place,  because  the  differences  in  the  chemical  compo- 
sition of  the  substratum  cause  continual  migrations. 
The  plasmodia  have  the  faculty  in  a  wonderful  way  of 
avoiding  harmful  substances,  and,  traversing  their 
substratum  in  all  directions,  of  taking  up  the  materials 
they  require. 

"When  the  internal  changes  have  proceeded  so  far 
that  the  plasmodia  approach  the  fructifying  condition, 
they  are  brought  by  the  negative  hydrotropism  which 
now  sets  in,  from  the  moist  parts  of  the  ground  in  the 
forest  or  wood  to  the  surface,  where  they  creep  up 
various  upright  objects,  often  only  forming  rigid  re- 
productive capsules  at  some  height  from  the  ground. 

"When  in  autumn  the  substratum  becomes  grad- 
ually colder  a  change  which  takes  place  from  the  sur- 


THE  FUNCTION  OF  CONSCIOUSNESS.  503 

face  downwards,  the  plasmodia  migrate  into  deeper 
regions  still  having  a  higher  temperature.  When  the 
cooling  proceeds  very  gradually,  which  especially  hap- 
pens in  large  tan-heaps,  the  plasmodia  may,  in  their 
migration  reach  somewhat  considerable  depths,  where 
they  then  change  into  sclerotia.  To  find  the  sclerotia 
of  ^Ethalium  in  winter  it  is,  therefore,  not  seldom 
necessary  to  search  through  the  mass  of  tan  to  a  depth 
of  several  feet.  When  the  temperature  again  begins 
to  rise,  the  sclerotia  again  germinate,  and  movement 
in  the  opposite  direction  takes  place  from  the  deeper 
and  cooler  parts  to  the  upper  portions  already  warmed. 

"In  the  locomotion  of  the  Myxomycetes,  then,  we 
see  extremely  interesting  cases  of  movements  due  to 
stimulation.  Heliotropism,  geotropism,  hydrotropism, 
trophotropism,  in  general,  are  stimulus-movements, 
and  ultimately  all  growth  depends  on  stimulus-move- 
ment. It  is  the  most  primitive  kind  of  protoplasmic 
movement.  Stimuli  in  fixed  directions  and  constantly 
repeated,  produced,  but  only  secondarily,  fixed  paths 
of  conduction,  and  responses  of  a  quite  definite  kind 
(reflexes).  Thus  arose  nerves,  .and  finally  apparatus 
for  stirring  up  stimuli,  arose  sensation  and  will — as 
acquired  and  inherited  faculties." 

In  this  lowest  type  of  organic  movement  it  is  diffi- 
cult to  discern  any  cause  for  it  different  from  those 
which  actuate  higher  organisms.  What  form  of  inor- 
ganic energy  can  be  cited  as  sufficient  to  cause  the 
organism  to  change  its  position  with  regard  to  stimuli 
to  self-preservation,  and  without  regard  to  gravita- 
tion, or  any  known  form  of  attraction  or  repulsion? 
In  the  Fuligo  (tan  flowers)  a  most  pronounced  ex- 
ample of  designed  movement  has  been  observed. 
This  form,  in  the  amrebula  stage,  will,  according 


504    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

to  H.  J.  Carter,  "confine  itself  to  the  water  of  the 
watch-glass  in  which  it  may  be  placed,  when  away 
from  the  sawdust  and  chips  of  wood  among  which  it 
has  been  living  ;  but  if  the  watch-glass  be  placed  upon 
the  sawdust  it  will  very  soon  make  its  way  over  the 
side  of  the  watch-glass  and  get  to  it. "  This  act  probably 
depends  on  a  sense-perception  of  the  presence  and  posi- 
tion of  the  tan-bark,  and  of  a  feeling  of  desire  to  reach 
it.  This  may  have  been  due  to  a  sense  of  discomfort 
due  to  the  surrounding  water,  or  to  a  recollection  of 
superior  comfort  associated  with  the  tan-bark. 

Ordinary  observation  of  most  animals  leads  to  the 
belief  that  their  movements  are  provoked  by  sensa- 
tions, as  of  hunger,  thirst,  temperature,  etc.;  also  of 
sight,  hearing,  smell,  etc.,  when  they  possess  those 
senses.  There  are  physiologists  who  deny  that  such 
is  the  case,  but  I  must  insist  on  the  importance  of  a 
psychological  rather  than  a  physiological  study  of  ani- 
mals as  a  most  important  source  of  information  in 
this  direction.  The  students  of  dead  or  mutilated 
animals  miss  important  evidence  as  to  the  phenomena 
of  consciousness.  The  attempt  has  been  made  to 
identify  hunger,  for  instance,  with  chemical  energy,  a 
proposition  which  is  simply  irrational.  It  may  be  none 
the  less  true,  however,  that  hunger  is  a  necessary  con- 
comitant of  a  molecular  condition.  Observation  on 
living  animals  shows  in  the  most  conclusive  manner 
that  by  far  the  greater  number  of  species  are  capable 
of  the  performance  of  acts  in  response  to  new  situations 
and  circumstances  for  the  performance  of  which  no 
automatic  mechanism  exists.  Memory  is  clearly  pres- 
ent in  them,  and,  as  a  consequence,  judgments  are 
formed  which  determine  the  succeeding  acts.  The 
process,  be  it  ever  so  simple,  is  "representative, "and 


THE  FUNCTION  OF  CONSCIOUSNESS.  505 

thus  a  mental  act,  at  least  one  stage  beyond  sense- 
impression.  The  doctrine  that  conscious  states  have 
preceded  organisms  in  time  and  evolution  I  have  called 
archaesthetism.  It  seems  to  have  been  first  clearly  for- 
mulated by  Erasmus  Darwin,  who  believed  that  growth 
has  been  stimulated  by  "irritations  "  (of  hunger,  thirst, 
etc.)  and  by  the  pleasurable  sensations  attending  those 
irritations,  and  by  exertions  in  consequence  of  painful 
sensations,  similar  to  those  of  hunger  and  suffocation,"1 
etc. 

The  weakness  of  the  doctrine  of  archaesthetism  con- 
sists in  our  ignorance  of  the  characters  of  the  Proto- 
zoa, with  respect  to  the  presence  or  absence  of  con- 
sciousness or  sensation.  While  many  of  the  acts  of 
these  low  organisms  need  not  be  explained  by  suppos- 
ing its  presence,  others  seem  to  be  impossible  without 
it.  We  are,  however,  led  to  infer  its  presence  rather 
on  uniformitarian  grounds,  than  by  any  certainty  of 
explanation  of  the  phenomena.  We  can  trace  sensa- 
tion so  far  down  in  the  scale  of  animal  life,  that  it 
seems  unreasonable  to  deny  its  presence  when  the 
same  phenomena  are  exhibited  by  the  Protozoa.  We 
are  confirmed  in  our  belief  in  the  presence  of  sensation 
in  these  low  forms,  by  the  knowledge  that  reflex  acts 
are  the  product  of  conscious  acts,  whereas  we  have  no 
evidence  that  conscious  acts  are  the  product  of  the  re- 
flex. 

Although  it  is  frequently  alleged  or  assumed  that 
designed  conscious  acts  are  the  product  of  reflexes,  no 
one  has  yet  shown  how  this  is  possible.  On  the  other 
hand,  the  development  of  automatic  acts  out  of  con- 
scious ones  is  of  ordinary  occurrence,  and  is  known 
under  the  name  of  education. 

\Zoonomia  XXXIX.;  3  ;  Osborn.  From,  the  Greeks  to  Darwin,  p.  148, 


506    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

The  relation  of  consciousness  to  the  physical  basis 
is  as  yet  a  profound  mystery,  but  that  they  exercise 
over  each  other  a  definite  mutual  control  is  unques- 
tionable. The  processes  which  produce  thought,  as 
conception,  judgment,  etc.,  are,  however,  not  qualita- 
tively related  to  the  amount  of  nutritious  proteids 
consumed  in  the  central  nervous  system,  but  only 
quantitatively;  yet  it  is  the  outcome  of  these  processes 
that  directs  animal  movements,  when  they  are  not  auto- 
matic. In  other  words,  the  forms  of  thought,  which 
have  no  weight,  direct  the  movements  of  muscles, 
which  have  weight.  This  is  not  in  accord  with  the 
doctrine  of  the  correlation  of  energy.  But  what  has 
the  formation  of  a  concept,  or  the  development  of  a 
judgment,  to  do,  per  se,  with  the  correlation  of  energy? 
I  may  give  this  idea  a  more  definite  expression  by  the 
following  diagram  : x 


AFFIRMATIVE. 

NEGATIVE. 

I 

5 

2 

6 

3 

4 

AFFIRMATIVE. 

NEGATIVE. 

I 

3 

2 

4 

5 

6 

Let  each  square  represent  the  grammes  of  energy 
necessary  for  the  maintenance  in  consciousness  of  six 
propositions.  Judgment  issues  from  the  side  of  the 
predominating  number  of  propositions.  They  arrange 
themselves  in  consciousness  in  accordance  with  their 
qualities,  in  two  aggregations  represented  by  columns 
in  the  squares.  Now  if  they  arrange  themselves  in 
four  affirmative  and  two  negative,  as  in  square  i,  the 


IThis  is  in  explanation  of  the  same  proposition  as  stated  by  me  in  the 
Proceedings  of  the  American  Philosophical  Society,  1889,  p.  504. 


THE  FUNCTION  OF  CONSCIOUSNESS.  507 

judgment  is  affirmative.  If,  on  the  other  hand,  they 
arrange  themselves  in  two  affirmative  and  four  nega- 
tive, as  in  square  2,  the  judgment  is  negative.  The 
energy  expended  in  the  two  cases  is  the  same.  So  also 
in  forming  different  concepts  from  the  same  set  of  par- 
ticular sense-impressions  or  memories.  Is  there  any  dif- 
ference in  the  energy  expended  in  forming  from  them 
the  concept  of  bigness  as  compared  with  that  of  red- 
ness? While,  therefore,  every  mental  process  is  ex- 
pensive as  a  whole,  the  mental  content  is  obedient  to 
the  forms  of  thought  rather  than  the  correlation  of 
energy.  This  is  what  mind  is.  While  it  is  doubtful 
whether  any  animal  below  man  can  form  a  concept 
(with  a  very  few  possible  exceptions),  the  formation 
of  simple  judgments  is  general.  Any  decision  based 
on  experience  is  a  judgment. 

In  order  to  render  this  proposition  clearer,  I  have 
formulated  it  in  the  following  language,  although  it  is 
possible  that  the  definition  of  energy  will  not  bear  the 
strain  of  the  statement. 

"The  formal  statement  of  this  phenomenon  may  be 
found  in  the  thesis,  that  energy  can  be  conscious.  If  true, 
this  is  an  ultimate  fact,  neither  more  nor  less  diffi- 
cult to  comprehend  than  the  nature  of  energy  or 
matter  in  their  ultimate  analyses.  But  how  is  such  a 
hypothesis  to  be  reconciled  with  the  facts  of  nature, 
where  consciousness  plays  a  part  so  infinitesimally 
small?  The  explanation  lies  close  at  hand,  and  has 
been  already  referred  to.  Energy  become  automatic  is 
no  longer  conscious,  or  is  about  to  become  unconscious. 
That  this  is  the  case  is  matter  of  every-day  observa- 
tion on  ourselves  and  on  other  animals.  What  the 
molecular  conditions  of  consciousness  are,  is  one  of 
the  problems  of  the  future,  and  for  us  a  very  interest- 


508   PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

ing  one.  One  thing  is  certain,  the  organization  of  the 
mechanism  of  habits  is  its  enemy.  //  is  clear  that  in 
animals,  energy,  on  the  loss  of  consciousness,  undergoes  a 
retrograde  metamorphosis. 

"To  regard  consciousness  as  the  primitive  condi- 
tion of  energy,  contemplates  an  order  of  evolution  in 
large  degree  the  reverse  of  the  one  which  is  ordinarily 
entertained.  The  usual  view  is,  that  life  is  a  deriva- 
tive from  inorganic  energies  as  a  result  of  high  or  com- 
plex molecular  organization,  and  that  consciousness 
(=  sensibility)  is  the  ultimate  outcome  of  the  nervous 
or  equivalent  energy  possessed  by  living  bodies.  The 
failure  of  the  attempts  to  demonstrate  spontaneous 
generation  will  prove,  if  continued,  fatal  to  this  theory. 
With  our  present  evidence  it  may  be  affirmed  that  not 
only  'has  life  preceded  organization,'  but  that  con- 
sciousness was  coincident  with  the  dawn  of  life  " 

The  facts  cited,  and  the  doctrines  defended  in  the 
preceding  pages  lead  to  one  inference  as  to  the  relation 
of  consciousness  to  its  physical  basis.  The  condition 
of  matter  necessary  to  the  maintenance  of  conscious- 
ness is,  in  the  language  of  morphology,  generalized',  in 
the  language  of  Chemistry,  neutral',  in  the  language  of 
physics,  non-equilibrated.  The  materialist  and  the  ani- 
mist  can  alike  agree  as  to  this  generalization.  The 
difference  between  the  two  positions  is  a  difference  of 
view  as  to  the  mutual  relations  of  the  two  members  of 
the  partnership.  Is  the  permanent  absence  of  equi- 
librium of  living  protoplasm  due  to  control  by  con- 
sciousness ?  or  is  consciousness  a  product  of  an  absence 
of  equilibrium,  which  is  due  to  chemical  and  physical 
action?  The  latter  proposition  is  untenable,  because 
the  inevitable  tendency  of  chemical  and  physical  ener- 
gies is  to  an  equilibrium.  Is,  therefore,  the  other  al- 


THE  FUNCTION  OF  CONSCIOUSNESS.  509 

ternative  true?  There  seems  to  be  no  escape  from  it, 
and  it  accords  also  with  our  personal  human  experi- 
ence of  the  agency  of  conscious  states  in  our  various 
activities,  physical  and  mental. 

2.  THE  EFFECTS  OF  CONSCIOUSNESS. 

From  the  facts  cited  it  is  evident  that  sensation 
(consciousness)  has  preceded  in  time  and  in  history, 
the  evolution  of  the  greater  part  of  plants  and  animals, 
both  unicellular  and  multicellular.  It  appears  also 
that  if  kinetogenesis  be  true,  consciousness  has  been 
essential  to  a  rising  scale  of  organic  evolution. 

Animals  who  do  not  perform  simple  acts  of  self- 
preservation  must  necessarily  perish  sooner  or  later. 
In  fact  it  is  impossible  to  understand  how  the  lowest 
forms  of  life,  utterly  dependent  as  they  are  on  physi- 
cal conditions  of  many  kinds,  should  not  have  been 
all  destroyed,  were  they  not  possessed  of  some  degree 
of  consciousness  under  stimuli  at  least.  And  the  case 
is  even  plainer  with  the  higher  forms.  We  have  only 
to  picture  to  ourselves  the  condition  of  a  vertebrate 
without  general  or  special  sensation,  to  perceive  how 
essential  consciousness  is  to  its  existence.  If  now,  as 
maintained  in  Chapter  IV.,  use  has  modified  struc- 
ture, and  so,  in  cooperation  with  the  environment,  has 
directed  evolution,  we  can  understand  the  origin  and 
development  of  useful  organs.  And  we  can  under- 
stand how  by  parasitism  or  other  mode  of  gaining  a 
livelihood  without  exertion,  the  adoption  of  new  and 
skilful  movements  would  become  unnecessary,  and 
consciousness  itself  would  be  seldom  aroused.  Con- 
tiued  repose  would  be  followed  by  subconsciousness, 
and  later  by  unconsciousness.  Such  appears  to  be  the 
history  of  degeneracy  everywhere,  and  such  is,  per- 


5io     PR  I  MAR  V  FA  CTORS  OF  ORGANIC  E  VOL  UTION. 

haps,  the  history  of  the  entire  vegetable  kingdom. 
From  their  ability  to  manufacture  protoplasm  from 
inorganic  substances,  plants  do  not  need  to  move 
about  in  search  of  food,  so  that  they  require  no  con- 
sciousness of  conditions  to  guide  their  movements. 
They  become  fixed,  and  their  entire  organization  be- 
comes monopolized  by  the  functions  of  nutrition  and 
reproduction.  Movements  rarely  occur,  and  when 
present  are  confined  to  those  of  one  part  of  the  struc- 
ture or  another.  They  are  mostly  rhythmic  or  rotary, 
and  very  seldom  exhibit  the  quality  of  impromptu  de- 
sign. The  satisfactory  explanation  of  those  that  ex- 
hibit general  design,  as  the  adaptation  for  transporta- 
tion often  seen  in  seeds,  may  be  chance  coincidence 
and  natural  selection. 

The  ascending  scale  of  development  of  intelligence 
observed  among  animals  is  strong  evidence  in  support 
of  the  hypothesis  here  outlined.  There  can  be  no 
doubt  that  in  the  long  run  the  most  intelligent  have 
survived.  They  have  survived  because  they  were 
capable  of  the  most  successful  designed  acts,  thus 
directing  their  movements  to  the  most  useful  ends. 
These  movements  ultimately  modified  their  structure 
usefully,  to  the  perfecting  of  mechanisms  in  every  way 
important  to  their  possessors.  This  much  having  been 
established  as  to  the  cause  of  anagenesis,  let  us  look 
more  closely  into  the  history  of  catagenesis. 

Movements  of  organic  beings  on  frequent  repeti- 
tion become  automatic,  reflex,  and  finally,  as  it  is 
termed,  organic.  This  means  the  running  down  of 
energy  through  various  grades,  beginning  with  the 
highest  or  conscious  stage,  and  ending  with  the  purely 
reflex,  which  is  as  unconscious  of  changes  in  the  en- 
vironment as  is  any  one  of  the  physical  energies.  The 


THE  FUNCTION  OF  CONSCIOUSNESS.  511 

conscious  stage  is  evidently  the  most  susceptible  to 
the  stimuli  of  the  environment,  and  the  process  of 
catagenesis  is  one  of  degeneracy  to  less  and  less  sensi- 
tive and  to  more  and  more  mechanical  conditions. 
The  resemblance  of  the  lowest  grade  of  organic  activ- 
ities to  physical  mechanical  energy  is  so  great  that  it 
is  almost  universally  supposed  by  evolutionists  to  be 
of  purely  mechanical  origin,  but  I  have  endeavored  to 
show  that  they  are  of  totally  different  origin,  and  that 
the  only  explanation  of  their  characteristics  is  the  hy- 
pothesis of  catagenesis. 

In  accordance  with  this  view,  the  automatic  "in- 
voluntary" movements  of  the  heart,  intestines,  repro- 
ductive systems,  etc.,  were  organized  in  primitive  and 
simple  animals  in  successive  states  of  consciousness, 
which  stimulated  "voluntary"  movements,  which  ulti- 
mately became  rhythmic;  whose  results  varied  with 
the  machinery  already  existing  and  the  material  at 
hand  for  use.  It  is  not  inconceivable  that  circulation 
may  have  been  established  by  the  suffering  produced 
by  an  overloaded  stomach  demanding  distribution  of 
its  contents.  The  structure  of  the  Infusoria  offers  the 
structural  conditions  of  such  a  process.  A  want  of 
propulsion  in  a  stomach  or  body-sack  occupied  with 
its  own  functions  would  lead  to  a  painful  clogging  of 
the  flow  of  its  products,  and  the  "voluntary"  contrac- 
tility of  the  body  or  tube-wall  being  thus  stimulated, 
would  at  some  point  originate  the  pulsation  necessary 
to  relieve  the  tension.  Thus  might  have  originated 
the  "contractile  vesicle"  or  contractile  tube  of  some 
protozoa ;  its  ultimate  product  being  the  mammalian 
heart.  So  with  reproduction.  Perhaps  an  excess  of 
assimilation  in  well-fed  individuals  of  the  first  animals 
led  to  the  discovery  that  self-division  constituted  a  re- 


5I2    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

lief  from  the  oppression  of  too  great  bulk.  With  the 
increasing  specialization  of  form,  this  process  would 
become  necessarily  localized  in  the  body,  and  growth 
would  repeat  such  resulting  structure  in  descent,  as 
readily  as  any  of  the  other  structural  peculiarities.  No 
function  of  the  higher  animals  bears  the  mark  of  con- 
scious origin  more  than  this  one,  as  consciousness  is 
still  one  of  the  conditions  of  its  performance.  While 
less  completely  " voluntary"  than  muscular  action,  it 
is  more  dependent  on  stimulus  for  its  initial  move- 
ments, and  does  not  in  these  display  the  unconscious 
automatism  characteristic  of  many  other  functions. 

There  remain,  however,  some  phenomena  which  do 
not  yield  so  readily  to  this  analysis.  First,  we  have  the 
conversion  of  inorganic  substances  into  protoplasm  by 
plants.  It  is  also  well  known  that  living  animal  or- 
ganisms act  as  producers,  by  conversion,  of  various 
kinds  of  inorganic  energy,  as  heat,  light,  sound,  electri- 
city, motion,  etc.  It  is  the  uses  to  which  these  forces  are 
put  by  the  animal  organism,  the  evident  design  in  the 
occasion  of  their  production,  that  gives  them  the  stamp 
of  organic  life.  We  recognize  the  specific  utility  of  the 
secretions  of  the  glands,  the  appropriate  distribution  of 
the  products  of  digestion  and  adaptation  of  muscular 
motion  to  many  uses.  The  increase  of  heat  to  protect 
against  depression  of  temperature  ;  the  light  to  direct 
the  sexes  to  each  other ;  the  electricity  as  a  defence 
against  enemies — display  unmistakably  the  same  util- 
ity. We  must  not  only  believe  that  these  functions 
of  animals  were  originally  used  by  them  under  stimu- 
lus, for  their  benefit,  but,  if  life  preceded  organism, 
that  the  mechanism  which  does  the  work  has  devel- 
oped as  the  result  of  the  animal's  exertions  under  stim- 
uli. This  will  especially  apply  to  the  mechanism  for 


THE  FUNCTION  OF  CONSCIOUSNESS.  513 

the  production  of  motion  and  sound.  The  production 
of  heat,  light,  chemism,  and  electricity  doubtless  re- 
sult from  molecular  aptitudes  inherent  in  the  constitu- 
tion of  protoplasm.  But  the  first  and  last  production 
of  even  these  phenomena  is  dependent  on  the  motions 
of  the  animal  in  obtaining  and  assimilating  nutrition. 
For  without  nutrition  all  energy  would  speedily  cease. 
Now  the  motion  required  for  the  obtaining  of  nutrition 
has  its  origin  in  the  sensation  of  hunger.  So,  even  for 
the  first  steps  necessary  to  the  production  of  inorganic 
forces  in  animals,  we  are  brought  back  to  a  primitive 
consciousness.  This  hypothesis  I  have  termed  Ar- 
chaesthetism. 

"It  maintains  that  consciousness  as  well  as  life 
preceded  organism,  and  has  been  the  primum  mobile  in 
the  creation  of  organic  structure.  This  conclusion 
also  flows  from  a  due  consideration  of  the  nature  of 
life.  I  think  it  possible  to  show  that  the  true  defini- 
tion of  life  is,  energy  directed  by  sensibility,  or  by  a  mech- 
anism which  has  originated  under  the  direction  of  sensi- 
bility. If  this  be  true,  the  two  statements  that  life  has 
preceded  organism,  and  that  consciousness  has  pre- 
ceded organism  are  coequal  expressions. 

"Granting  the  existence  of  living  protoplasm  on 
the  earth,  there  is  little  doubt  that  we  have  some 
of  its  earliest  forms  still  with  us.  From  these  sim- 
plest of  living  beings  both  vegetable  and  animal  king- 
doms have  been  derived.  But  how  was  the  distinc- 
tion between  the  two  lines  of  development,  now  so 
widely  divergent,  originally  produced  ?  The  process 
is  not  difficult  to  imagine.  The  original  plastid  dis- 
solved the  salts  of  the  earth  and  appropriated  the  gases 
of  the  atmosphere  and  built  for  itself  more  protoplasm. 
Its  energy  was  sufficient  to  overcome  the  chemism 


514    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

that  binds  the  molecules  of  nitrogen  and  hydrogen  in 
ammonia,  and  of  carbon  and  oxygen  in  carbonic  diox- 
ide. It  apparently  communicated  to  these  molecules 
its  own  method  of  being,  and  raised  the  type  of  energy 
from  the  polar  non-vital  to  the  adaptive  vital  by  the 
process.  Thus  it  transformed  the  dead  inorganic  world, 
perhaps  by  a  process  of  invasion,  as  when  a  fire  com- 
municates itself  from  burning  to  not  burning  combust- 
ible material.  Thus  it  has  been  doing  ever  since,  but 
it  has  redeposited  some  of  its  gathered  stores  in  vari- 
ous non-vital  forms.  Some  of  these  are  in  organic 
forms,  as  cellulose  ;  others  are  crystals  imprisoned  in 
its  cells  ;  while  others  are  amorphous,  as  waxes,  resins, 
and  oils.  But  consciousness  apparently  early  aban- 
doned the  vegetable  line.  Doubtless  all  the  energies 
of  vegetable  protoplasm  soon  became  automatic.  The 
plants  in  general,  in  the  persons  of  their  protist  ances- 
tors, soon  left  a  free-swimming  life  and  became  sessile. 
Their  lives  thus  became  parasitic,  more  automatic, 
and  in  one  sense  degenerate. 

11  The  animal  line  may  have  originated  in  this  wise. 
Some  individual  protists,  perhaps  accidentally,  de- 
voured some  of  their  fellows.  The  easy  nutrition  which 
ensued  was  probably  pleasurable,  and  once  enjoyed 
was  repeated,  and  soon  became  a  habit.  The  excess 
of  energy  thus  saved  from  the  laborious  process  of 
making  protoplasm  was  available  as  the  vehicle  of  con- 
sciousness and  motion.  From  that  day  to  this,  con- 
sciousness has  abandoned  few  if  any  members  of  the 
animal  kingdom.  In  many  of  them  it  has  specialized 
into  more  or  less  mind.  Organization  to  subserve  its 
needs  has  achieved  a  multifarious  development.  There 
is  abundant  evidence  to  show  that  the  permanent  and 
the  successful  forms  have  ever  been  those  in  which 


THE  FUNCTION  OF  CONSCIOUSNESS.  515 

motion  and  sensibility  have  been  preserved,  and  most 
highly  developed.1 

We  must  remember,  however,  that  in  the  matter 
of  the  evolution  of  plant-types  we  have  an  especial 
factor  in  the  influence  which  insects  have  exerted  on 
the  conditions  of  almost  all  of  their  organs.  Insects 
originated  early  in  geological  time,  and  have  closely 
accompanied  plants  in  their  evolution.  As  the  source 
of  the  food,  and  as  the  dwelling-places  of  great  num- 
bers of  insects,  they  have  been  subjected  to  a  class  of 
stimuli  and  strains  similar  to  those  which  animals  have 
experienced.  It  is  believed  that  the  forms  of  the  or- 
gans of  fructification  and  especially  of  the  flowers, 
have  been  greatly  modified  by  the  influence  of  insects.2 
The  general  evolution  of  plants,  however,  presents  us 
with  a  greater  predominance  of  physiogenetic  or  simple 
dynamical  conditions  over  the  bathmic,  than  in  the  case 
of  animals.  Thus  many  peculiarities  of  the  inflores- 
cence directly  result  from  the  shortening  of  the  axial 
growth  in  complementary  relation  to  the  increase  of 
peripheral  growth.  Such  is  evidently  the  origin  of 
flowers  themselves  ;  secondly  of  the  umbel  as  com- 
pared with  the  spike  or  panicle  and  finally  of  the  com- 
posite head  as  compared  with  the  other  modes  of  in- 
florescence. To  the  cohesion  of  the  elements  of  a 
whorl,  possible  only  in  the  case  of  an  abbreviated  axis, 
can  we  ascribe  the  formation  of  a  seed  vessel  from  dis- 
crete carpels,  and  a  gamopetalous  from  a  polypetalous 
corolla.  Degeneracy  or  specialization  is  to  be  seen 
everywhere,  as  in  the  abortion  of  ovules,  carpels,  and 
perianth. 

"Catagenesis  of  living  organisms  has  been  epito- 

\Origin  of  the  Fittest,  p.  428,  432. 
2Henslow. 


5i6    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

mized  in  the  following  language  :  'Evolution  of  living 
types  is  then  a  succession  of  elevation  of  platforms, 
on  which  succeeding  ones  have  built.  The  history  of 
one  horizon  of  life  is  that  its  own  completion  but  pre- 
pares the  way  for  a  higher  one,  furnishing  the  latter 
with  conditions  of  a  still  further  development.  Thus 
the  vegetable  kingdom  died,  so  to  speak,  that  the  ani- 
mal kingdom  might  live,  having  descended  from  an  ani- 
mal stage  to  subserve  the  function  of  food  for  animals. 
The  successive  types  of  animals  first  stimulated  the 
development  of  the  most  susceptible  to  the  conflict, 
in  the  struggle  for  existence,  and  afterwards  furnished 
them  with  food.'  In  the  occupation  of  the  world's 
fields,  the  easiest  and  nearest  at  hand  have  been  first 
occupied,  and  successively  those  which  were  more  dif- 
ficult. The  digging  animals  are  generally  those  which 
first  abandoned  the  open  field  to  more  courageous  or 
stronger  rivals  ;  and  they  remain  to  this  day  generally 
of  low  type  compared  with  others  of  their  classes  (e.  g. 
Monotremata,  Gltres,  Insectivord}.  All  occupations  have 
been  filled  before  that  one  which  requires  the  greatest 
expenditure  of  energy,  i.  e.  mental  activity.  But  all 
other  modes  of  life  have  fallen  short  of  this  one  in  giv- 
ing the  supremacy  over  nature. " 

We  now  approach  an  explanation  of  the  phenome- 
non of  anagenesis.  Why  should  evolution  be  pro- 
gressive in  the  face  of  universal  catagenesis?  No  other 
ground  seems  discoverable  but  the  presence  of  sensa- 
tion or  consciousness,  which  is,  metaphysically  speak- 
ing, the  protoplasm  of  mind.  The  two  sensations  of 
hunger  and  sex,  have  furnished  the  stimuli  to  internal 
and  external  activity,  and  memory,  or  experience  with 
natural  selection,  have  been  the  guides.  Mind  and 
body  have  thus  developed  contemporaneously  and 


THE  FUNCTION  OF  CONSCIOUSNESS.  517 

have  reacted  mutually.     Without  the  cooperation  of 
all  these  factors,  anagenesis  seems  impossible. 

From  this  point  of  view  the  study  of  the  evolution 
of  mind  and  its  relation  to  the  organic  world  assumes 
a  new  importance.  Circumstances  have  forbidden  my 
entering  on  this  subject  in  the  present  volume,  but  I 
hope  to  be  able  to  devote  especial  attention  to  it  at  a 
future  time.  One  fundamental  postulate  of  mental 
evolution  may,  however,  be  mentioned  here.  That  is, 
as  Spencer  has  pointed  out,  the  instinct  of  hunger  is 
at  the  basis  of  the  activity  which  has  developed  the 
intelligence,  while  that  of  sex  is  at  the  basis  of  the  de- 
velopment of  the  altruistic  or  social  instincts  and  affec- 
tions. With  this  proposition  I  leave  this  interesting 
part  of  the  doctrine  of  evolution. 


CHAPTER  XI.— THE  OPINIONS  OF 
NEOLAMARCKIANS. 


T  AMARCK  ascribed  some  of  the  evolutionary  changes 
JL/  of  structure  to  changes  in  the  environment,  some 
to  the  motions  of  organic  beings,  and  others  to  both 
combined.1  Spencer  in  18652  devoted  a  short  chapter 
to  the  effect  of  motion  in  producing  variations,  and 
specified  the  mechanical  effect  of  flexure  in  producing 
segmentation  of  the  vertebral  column.  The  present 
writer  in  1871®  insisted  on  the  importance  of  motion 
as  a  factor  in  determining  growth,  and  in  1872*  I  ap- 
proached the  subject  more  definitely  in  the  following 
language  :  "  The  first  physical  law  is  that  growth  force 
.  .  .  must  develop  extent  in  the  direction  of  least  re- 
sistance, and  density  on  the  side  of  greatest  resist- 
ance." In  1877  Ryder  further  applied  the  principle 
of  motion  to  the  origin  of  structural  changes,  chiefly 
reduction  of  digits,  in  the  feet  of  Mammalia  in  lan- 
guage5 which  I  have  quoted  on  page  311. 

\Philosophie  Zoologique,  Chap.  VII.,  1809;  translation  in  American  Nat- 
uralist for  1888. 

2 Principles  of  Biology ;  II.,  pp.  167  and  195. 

^Proceeds.  Amer.  Philosoph.  Soc.,  1871,  p.  259.  Origin  of  the  Fittest,  1887,  p. 
210. 

IPenn  Monthly  Magazine,  July,  1872.     Origin  of  the  Fittest,  1887,  p.  30. 

5  American  Naturalist,  1877,  p.  607. 


THE  OPINIONS  OF  NRO-LAMARCKIANS.          519 

In  the  same  year,  in  discussing  the  origin  of  the 
great  development  of  the  incisor  teeth  in  the  Roden- 
tia,1  Professor  Ryder,  in  summing  up,  ventured  "the 
reflection  that  the  more  severe  strains  to  which  they 
were  subjected  by  enforced  or  intelligently  assumed 
changes  of  habit,  were  the  initiatory  agents  in  causing 
them  to  assume  their  present  forms,  such  forms  as 
were  best  adapted  to  resist  the  greatest  strains  with- 
out breaking."  In  1878  the  writer2  advanced  the  fol- 
lowing proposition  :  "Change  of  structure  is  seen  to 
take  place  in  accordance  with  the  mechanical  effect  of 
three  kinds  of  motion,  viz.,  by  friction,  pressure,  and 
strain."  In  the  same  year  Professor  Ryder  went  into  a 
discussion  of  the  specific  application  of  strains  in  the 
evolution  of  the  dental  types  of  the  diplarthrous  Un- 
gulata,  and  prepared  the  field  for  work  in  the  Rodentia 
and  Proboscidia.3  In  1879  the  writer  gave  mechan- 
ical reasons  for  the  reduction  of  the  sectorial  teeth  of 
Carnivora  to  one,  and  for  their  present  position  in  the 
jaws.4  In  1881  the  writer6  described  the  specific  ac- 
tion of  impacts  and  strains  in  the  production  of  the 
existing  characters  of  the  articulations  of  the  limbs  in 
the  higher  Mammalia.  In  1887  the  same  subject,  to- 
gether with  that  of  the  mechanical  origin  of  the  char- 
acters of  the  molar  teeth,  was  more  fully  investigated 
in  a  paper  on  the  Perissodactyla.6  In  1888  the  writer 
published  a  paper  on  the  mechanical  origin  of  the  sec- 
torial teeth  of  the  Carnivora,7  one  on  the  mechanical 

1  Proceeds.  Phila.  Acad.,  1877,  p.  318. 

2  American  Naturalist,  January,  1878.    Origin  of  the  Fittest,  p.  354. 
3 Proceeds.  Phila.  Acad.,  1878,  p.  45. 

4  American  Naturalist,  -March,  1879. 

5  American  Naturalist,  April  and  June,  1881. 

6  American  Naturalist,  1887,  pp.  985,  1060. 

7  Read  before  the  American  Association  for  the  Advancement  of  Science, 
New  York,  1887,  p.  254. 


520    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

origin  of  the  peculiar  dentition  of  the  Glires,1  and  a 
third  on  the  mechanical  origin  of  the  dentition  of  the 
Amblypoda.2  In  1889  I  discussed  the  mechanical 
causes  of  the  structures  of  the  elbow  and  other  joints 
in  the  Artiodactyla  and  the  origin  of  the  peculiar  in- 
tervertebral  articulations  in  that  order.3  In  the  same 
year  I  published  a  resume  of  the  work  done  on  this 
subject  with  reference  to  the  Mammalia.4  Since  that 
time  important  contributions  to  the  subject  have  been 
made  by  Ryder,  Osborn,  Wortman,  Dall,  Jackson, 
and  others,  to  which  reference  will  now  be  made. 

Hyatt  says  as  a  result  of  his  exhaustive  studies 
of  the  phylogeny  of  the  Cephalopoda5;  "The  ac- 
tion of  physical  changes  takes  effect  upon  an  irrit- 
able, plastic  organism  which  necessarily  responds  to 
external  stimulants  by  an  internal  reaction  or  effort. 
This  action  from  within  upon  the  parts  of  organisms 
modifies  their  hereditary  forms  by  the  production  of 
new  growths  or  changes,  which  are  therefore  adapted 
or  suitable  to  the  conditions  of  the  habitat,  and  are 
therefore  physiologically  and  organically  equivalent  to 
the  physical  agents  and  forces  from  which  they  directly 
or  indirectly  originated.  In  so  far  then,  as  causes  and 
habits  are  similar,  they  probably  produce  representa- 
tion or  morphological  equivalence  in  different  series  of 
the  same  type  in  similar  habitats  :  and  in  so  far  as 
they  are  different,  they  probably  produce  the  differen- 

1  American  Naturalist,  January,  1888,  p.  3. 

2  Proceeds.  Amer.  Philosoph.  Soc.,  1888,  p.  80. 

3  American  Naturalist ',  March,  1889. 

4  The  American  Journal  of  Morphology,  September,  1889,  pp.  137-277,  "  On 
the  Mechanical  Causes  of  the  Development  of  the  Hard  Parts  of  the  Mam- 
malia." 

5  The  Genesis  of  the  Arietida;,  by  Alpheus  Hyatt ;  Smithsonian  Contribu- 
tions to  Knowledge,  and  Memoirs  of  the  Museum  of  Comparative  Zodlogy,  Vol. 
XVI.,  No.  3,  1889. 


THE  OPINIONS  OF  NEO-LAMARCKIANS          521 

tials  which  distinguish  series  and  groups  from  each 
other." 

Packard1  in  discussing  the  causes  of  the  blindness 
of  cave  animals,  says:  "Such  a  phrase  as  <  natural 
selection,'  we  repeat  does  not  to  our  mind  definitely 
bring  before  us  the  actual  working-causes  of  the  evo- 
lution of  these  cave  organisms,  and  no  one  cause  can 
apparently  account  for  the  result.  The  causes  are 
'  change  in  the  environment,'  disuse  of  certain  organs  ; 
'adaptation/  ' isolation/  and  ' heredity'  operating  to 
secure  for  the  future  the  permanence  of  the  newly  orig- 
inated forms  as  long  as  the  physical  conditions  remain 
the  same." 

In  1889,  Ryder  described  the  ontogenetic  origin  of 
the  articulations  of  the  cartilaginous  fin-rays  of  the 
Salmo  fontinalis,  and  used  the  facts  observed  as  evi- 
dence that  these  articulations  are  due  to  the  mechan- 
ical strain  experienced  by  the  rays  in  use  as  motors  of 
the  body  of  the  fish  in  the  water.2 

Prof.  H.  F.  Osborn  in  i8go3  discussed  thoroughly 
the  mechanical  causes  for  the  displacement  of  the  ele- 
ments of  the  feet  of  the  ungulate  Mammalia  from 
linear  to  alternating  relations.  (See  antea,  p.  299.) 
In  an  article  in  Nature^  the  same  distinguished  natu- 
ralist remarks:  "The  following  views  are  adopted 
from  those  held  by  Cope  and  others,  so  far  as  they  con- 
form to  my  own  observations  and  apply  to  the  class 
of  variations  which  come  within  the  range  of  paleon- 
tological  evidence.  In  the  life  of  the  individual,  adap- 

l"On  the  Cave  Fauna  of  North  America,"  Memoirs  of  the  U.  S.  National 
Academy  of  Sciences,  IV,  pt.,  I.,  p.  137. 

^Proceedings  of  the  American  Philosophical  Society,  1889,  p.  546. 

3  Transactions  of  'the  American  Philosophical  Society,  XVI.,  February,  1890, 
P-  531- 

^January  9,  1890,  p.  277. 


522    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

tation  is  increased  by  local  and  general  metatrophic 
changes  of  necessity  correlated,  which  take  place  most 
rapidly  in  the  regions  of  least  perfect  adaptation,  since 
here  the  reactions  are  greatest ;  the  main  term  of  vari- 
ation is  determined  by  the  slow  transmission,  not  of 
the  full  increase  of  adaptation,  but  of  the  disposition 
to  adaptive  atrophy  or  hypertrophy  at  certain  points ; 
the  variations  thus  transmitted  are  accumulated  by  the 
selection  of  the  individuals  in  which  they  are  most 
marked,  and  by  the  extinction  of  inadaptive  varieties 
or  species ;  selection  is  thus  of  the  ensemble  of  new 
and  modified  characters.  Finally,  there  is  sufficient 
paleontological  and  morphological  evidence  that  ac- 
quired characters  in  the  above  limited  sense,  are  trans- 
mitted. .  .  .  Excepting  in  two  or  three  side-lines  the 
teeth  of  all  the  Mammalia  have  passed  through  closely 
parallel  early  stages  of  evolution,  enabling  us  to  formu- 
late a  law :  The  new  main  elements  of  the  crown  make 
their  appearance  at  the  first  points  of  contact,  and  chief 
points  of  wear  of  the  teeth  in  preceding  periods.  What- 
ever may  be  true  of  spontaneous  variations  in  other 
parts  of  the  organism,  these  new  cusps  arise  in  the 
perfectly  definite  lines  of  growth.  .  .  .  Now,  after  ob- 
serving these  principles  operating  in  the  teeth,  look  at 
the  question  enlarged  by  the  evolution  of  parallel  spe- 
cies of  the  horse  series  in  America  and  Europe,  and 
add  to  the  development  of  the  teeth  what  is  observed 
in  progress  in  the  feet.  Here  is  the  problem  of  corre- 
lation in  a  stronger  form  even  than  that  presented  by 
Spencer  and  Romanes.  To  vary  the  mode  of  state- 
ment :  what  must  be  assumed  in  the  strict  application 
of  the  selection-theory?  (0)  that  variations  in  the  lower 
molars  correlated  with  coincident  variations  of  reversed 
patterns  in  the  upper  molars,  these  with  metamorpho- 


THE  OPINIONS  OF  NEO-LAMARCKIANS.          523 

sis  in  the  premolars  and  pocketing  of  the  incisor- 
enamel  ;  (fr)  all  new  elements  and  forms  at  first  so 
minute  as  to  be  barely  visible,  immediately  selected 
and  accumulated;  (Y)  in  the  same  individuals  favor- 
able variations  in  the  proportions  of  the  digits  involv- 
ing readjustments  in  the  entire  limbs  and  skeleton,  all 
coincident  with  those  in  the  teeth  \  (*/)  finally,  all  the 
above  new  variations,  correlations,  and  readjustments 
not  found  in  the  hereditary  germ-plasm  of  one  period, 
but  arising  fortuitously  by  the  union  of  different  strains, 
observed  to  occur  simultaneously  and  to  be  selected  at 
the  same  rate  in  the  species  of  the  Rocky  Mountains, 
the  Thames  Valley,  and  Switzerland  !  These  assump- 
tions, if  anything,  are  understated. " 

I  have  already  referred  to  the  contribution  by  Dall 
to  the  doctrine  of  kinetogenesis  which  has  resulted 
from  his  investigations  of  the  origin  of  the  characters 
of  the  lamellibranchiate  (or  pelecypod)  Mollusca.1  He 
observes  :  "In  reflecting  upon  the  origin  of  the  com- 
plicated mechanical  arrangements  in  bivalves  which 
we  call  the  hinge,  I  have  come  to  the  conclusion  that 
here,  as  in  the  cases  of  the  mammalian  foot  and  tooth 
elaborated  so  clearly  by  Cope  and  Ryder,  we  have  the 
result  of  influences  of  a  mechanical  nature  operating 
upon  an  organ  or  apparatus  in  the  process  of  develop- 
ment. .  .  .  The  shell  is  in  one  sense  the  product  of  se- 
cretion from  the  mantle,  as  the  mammalian  tooth  is 
derived  from  the  ectoderm  of  the  jaw,  or  the  skeleton 
from  the  periosteum  and  cartilages.  Both  are  that 
and  much  more.  It  would  be  as  reasonable  to  say 
that  a  steam  boiler  in  process  of  construction  is  the 
product  of  the  boy  inside  who  holds  the  rivet-heads, 
as  to  claim  that  the  shell  has  no  more  significance 

3  American  Journal  of  Science  and  Arts,  December,  1889,  p.  447. 


524    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

than  is  implied  in  the  term  ' secretion  of  the  mantle.' 
The  original  theoretic  protoconch  may  have  been  so, 
but  as  soon  as  it  came  into  being,  its  development  was 
governed  by  the  physical  forces  impinging  upon  it 
from  all  sides,  and  through  it  influencing  the  growth 
and  structure  of  the  soft  parts  beneath.  The  gastropod 
shell  is  the  result  of  the  action  and  reaction  between 
the  physical  forces  of  the  environment,  and  the  evolu- 
tionary tendencies  of  the  organic  individual.  In  the 
pelecypod  we  have  the  mechanical  stresses  and  reac- 
tions of  one  valve  upon  the  other,  added  to  the  cate- 
gory of  influences.  To  some  extent  it  is  doubtless  as 
true  that  the  animal  is  moulded  by  its  shell,  as  it  is 
that  the  shell  is  shaped  by  the  soft  parts  of  the  ani- 
mal." 

Dr.  Dall  in  an  able  paper  on  the  "Dynamic  In- 
fluences in  Evolution,"  read  before  the  Biological  So- 
ciety of  Washington,  March  8,  1890,  writes  thus  forci- 
bly: 

"It  is  often  assumed,  in  discussing  variation,  that 
the  possibility  of  variation  is  equal  in  every  direction. 
A  consideration  of  the  dynamic  conditions  of  life  show 
that  this  is  not  the  case,  or,  at  least,  if  we  grant  its 
theoretic  truth,  in  practice  it  can  never  be  true.  Un- 
der any  conditions  which  would  permit  it,  the  result- 
ing organic  forms  would  have  to  pass  their  existence 
in  constant  rotation.  The  moment  that  any  one  of 
them  came  to  rest,  it  would  begin  to  be  subjected  to 
unequal  stresses  relatively  to  its  different  parts.  Light, 
gravity,  friction,  opportunities  for  nutrition,  would  be 
unequally  distributed,  with  the  result  of  forcing  an 
unequal  growth,  development,  and  specialization  of 
its  regions.  Inequality  of  form  once  established,  if  it 
were  a  moving  organism,  friction  and  resistance  of  the 


THE  OPINIONS  OF  NEO-LAMARCKIANS.          525 

circumambient  medium,  would  confirm  the  inequality, 
and  put  individuals  of  its  kind  at  a  disadvantage  when 
they  varied  towards  the  original  shape." 

This  is  an  excellent  statement  of  kinetogenesis  in 
concentrated  form. 

Prof.  A.  S.  Packard  in  an  important  essay  "On 
the  Evolution  of  the  Bristles,  Spines,  and  Tubercles 
of  Certain  Caterpillars,"  etc.,  remarks  as  follows:1 
"The  Lamarckian  factors  (i)  of  change  (both  direct 
and  indirect)  in  the  milieu,  (2)  need,  (3)  habit,  and  the 
now  generally  adopted  principle  that  a  change  of  func- 
tion induces  change  in  organs,  and  in  some  or  many 
cases  actually  induces  the  hypertrophy  and  specialisa- 
tion of  what  otherwise  would  be  indifferent  parts  or 
organs.  These  factors  are  all  important  in  the  evolu- 
tion in  the  colors,  ornaments,  and  outgrowths  from 
the  cuticle  of  caterpillars.  .  .  . 

"So  far  as  I  am  aware  no  one  has  suggested  why 
these  horns  and  high  tubercles  and  often  pencils  of 
hairs  are  restricted  to  these  particular  segments.  As 
a  partial  explanation  of  the  reason,  it  may  be  stated 
that  the  presence  of  these  high  tubercles,  etc.,  is  cor- 
related with  the  absence  of  abdominal  legs  on  the  seg- 
ments bearing  the  former.  It  will  also  be  noticed  that 
in  walking  the  apodous  segments  of  the  caterpillar  are 
more  elevated  and  prominent  than  those  to  which  the 
legs  are  appended.  They  tend  to  bend  or  hump  up, 
particularly  the  first  and  the  eighth  abdominal,  the 
ninth  segment  being  reduced  to  a  minimum,  and  the 
tenth  simply  represented  by  the  suranal  and  paranal 
plates,  together  with  the  last  pair  of  legs. 

"As  is  well  known,  the  loopers  or  geometrid  worms, 
while  walking  elevate  or  bend  up  the  part  of  the  body 

I  Proceedings  of  the  Boston  Society  of  Natural  History,  1890,  p.  493,  510-513. 


526    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

situated  between  the  last  thoracic  and  first  pair  of  ab- 
dominal legs,  which  are  appended  to  the  seventh 
euomere.  Now  in  the  larva  of  Nematocarpa  filament  aria 
which  bears  two  pairs  of  remarkable  filamental  tuber- 
cles rolled  up  at  the  end,  it  is  certainly  very  sugges- 
tive that  these  are  situated  on  top  of  the  loop  made 
by  the  caterpillar's  body  during  progression,  the  first 
pair  arising  from  the  second,  and  the  hinder  pair  from 
the  fourth  abdominal  segment. 

"  It  seems,  therefore,  that  the  humps  or  horns  arise 
from  the  most  prominent  portions  of  the  body,  at  the 
point  where  the  body  is  most  exposed  to  external  stim- 
uli ;  and  the  force  of  this  is  especially  seen  in  the  con- 
spicuous position  of  those  tubercles  which  are  volun- 
tarily made  to  nod  or  so  move  as  to  frighten  away 
other  creatures.  Perhaps  the  tendency  of  these  seg- 
ments to  loop  or  hump  up,  has  had  a  relation  of  cause 
and  effect  in  inducing  the  hypertrophy  of  the  dermal 
tissues  entering  into  the  composition  of  the  tubercles 
or  horns." 

Prof.  W.  B.  Scott1  says  :  "To  sum  up  the  results 
of  our  examination  of  certain  series  of  fossil  mammals, 
one  sees  clearly  that  transformation,  whether  in  the 
way  of  the  addition  of  new  parts  or  the  reduction  of 
those  already  present,  acts  just  as  if  the  direct  action 
of  the  environment  and  the  habits  of  the  animal  were 
the  efficient  cause  of  the  change,  and  any  explanation 
which  excludes  the  direct  action  of  such  agencies  is 
confronted  by  the  difficulty  of  an  immense  number  of 
the  most  striking  coincidences.  ...  So  far  as  I  can  see 
the  theory  of  determinate  variations  and  of  use-inheri- 
tance, is  not  antagonistic,  but  supplementary  to  nat- 
ural selection,  the  latter  theory  attempting  no  explana- 

1  American  Journal  of  Morphology ,  1891,  pp.  395,  398. 


THE  OPINIONS  OF  NEO-LAMARCKIANS.          527 

tion  of  the  causes  of  variation.  Nor  is  it  pretended  for 
a  moment  that  use  and  disuse  are  the  sole  or  even  the 
chief  factors  in  variation." 

European  authors,  partly  from  their  less  favorable 
situation  for  the  obtaining  of  paleontologic  evidence, 
have  not  contributed  as  much  as  Americans  to  the 
doctrine  of  bathmogenesis.  Nevertheless,  in  England 
Spencer,  Cunningham,  Henslow,  and  others  have  sus- 
tained this  doctrine,  and  in  France  Giard  and  Edmond 
Perrier,  and  in  Germany,  Semper,  Eimer,  and  others, 
who  lean  principally  in  their  writings  to  its  physio- 
genetic  aspect.  Says  Eimer  : 1 

"According  to  my  conception,  the  physical  and 
chemical  changes  which  organisms  experience  during 
life,  through  light  or  want  of  light,  air,  warmth,  cold, 
moisture,  food,  etc.,  and  which  they  transmit  by  her- 
edity, are  the  primary  elements  in  the  production  of 
the  manifold  variety  of  the  organic  world,  and  in  the 
origin  of  species.  From  the  materials  thus  supplied, 
the  struggle  for  existence  makes  its  selection.  These 
changes,  however,  express  themselves  simply  as 
growth." 

Nageli  discards  completely  the  agency  of  natural 
selection,  and  sees  an  internal  "  Principle  of  Improve- 
ment" as  the  active  agent  in  evolution.  He  appar- 
ently includes  both  statogenesis  and  bathmogenesis  in 
his  conception.2  He  says  : 

"Such  internal  causes  must  necessarily  be  sup- 
posed merely  on  the  ground  that  modifications  or  vari- 
ations of  the  phyla  do  actually  take  place  in  definite 
directions,  are  not  irregular.  The  internal  causes  effect 

1  Organic  Evolution,  English  Translation,  1890,  p.  22. 

2 Mechanische  physiologische  Abstammungslehre,  C.   V.   Nageli,    Munich, 
1884. 


528    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

a  constant  alteration  of  the  phyla  in  definite  directions, 
towards  greater  perfection,  that  is,  towards  greater 
complexity."  Accordingly  Nageli  describes  his  theory 
of  internal  causes,  as  the  "Principle  of  Improvement." 
"Superficial  reasoners,"  he  says,  "have  pretended  to 
discover  mysticism  in  this.  But  the  principle  is  one 
of  a  mechanical  nature  and  constitutes  the  law  of  per- 
sistence of  motion  in  the  field  of  organic  evolution. 
Once  the  motion  of  evolution  is  started  it  cannot  cease, 
but  must  persist  in  its  original  direction." 

For  convenience  of  reference  I  give  a  list  of  pa- 
pers by  American  authors  on  this  subject.  European 
authors,  beginning  with  Lamarck,  and  including  Spen- 
cer, have  implicitly  included  in  their  theses  the  effects 
of  mechanical  strains  and  impacts  in  developing  the 
structures  of  animals.  Pick,  Henke,  Tornier,  and 
others  have  attempted  an  exact  demonstration  of  the 
manner  in  which  these  forms  of  mechanical  energy 
have  produced  the  results.  These  attempts  have  great 
merit  as  physiological  studies,  but  they  have  not  been 
used  by  their  authors  as  illustrations  of  specific  evolu- 
tion, owing  to  the  fact  that  they  have  not  carried  their 
researches  into  the  field  of  paleontology. 

LIST  OF  PAPERS  BY  AMERICAN  AUTHORS  WHO  HAVE 

CONTRIBUTED  TO  THE  EVIDENCE 

USED  IN  THIS  BOOK. 

1866.  Hyatt,  A.  Memoirs  of  the  Boston  Society  of  Natural  His- 
tory, p.  203.  On  the  Parallelism  Between  Stages  in  the 
Individual  and  those  in  the  Groups  of  Tetrabranchiata. 

1866.  Cope,  E.  D.  Transactions  of  the  American  Philosophical 
Society,  p.  398.  On  the  Cyprinidae  of  Pennsylvania. 

1871.  Cope,  E.  D.  Proceedings  of  the  American  Philosophical 
Society,  p.  259.  On  the  Method  of  Creation  of  Organic 
Types;  reprinted  in  Origin  of  the  Fittest,  1887,  pp.  210, 
195.  199- 


THE  OPINIONS  OF  NEO-LAMARCKIANS.          529 

1872.  Cope,  E.  D.  Perm  Monthly  Magazine,  May-July.  On  Evo- 
lution and  Its  Consequences ;  reprinted  in  Origin  of  the 
Fittest,  1887,  p.  30. 

1877.  Ryder,  J.  A.  American  Naturalist,  p.  607.  On  the  Laws 
of  Digital  Reduction. 

1877.  Ryder,  J.  A.     Proceedings  of  the  Academy  of  Natural  Sci- 

ences of  Philadelphia,  p.  314.  On  the  Significance  of  the 
Diameter  of  the  Incisors  of  the  Rodents. 

1878.  Cope,  E.  D.     American  Naturalist,  January.    The  Relation 

of  Animal  Motion  to  Animal  Evolution ;  reprinted  in 
Origin  of  the  Fittest,  1887,  p.  350. 

1878  Ryder,  J.  A.  Proceedings  Academy  Natural  Sciences,  Phila- 
delphia, p.  45.  On  the  Mechanical  Genesis  of  Tooth- 
Forms. 

1879.  Cope,  E.  D.     American  Naturalist,  March.     On  the  Origin 

of  the  Specialized  Teeth  of  the  Carnivora ;  Origin  of  the 
Fittest,  1887,  p.  363. 

(880.  Hyatt,  A.  Memoirs  Boston  Society  Natural  History,  Fiftieth 
Anniversary.  Genesis  of  the  Tertiary  Species  of  Planor- 
bis  at  Steinheim. 

1881.  Cope,  E.  D.  American  Naturalist,  April  and  June.  On  the 
Origin  of  the  Foot-Structures  of  the  Ungulates.  On  the 
Effect  of  Impacts  and  Strains  on  the  Feet  of  Mammalia  ; 
Origin  of  the  Fittest,  1887,  pp.  368,  373. 

1883.  Ryder,  J.  A.  Popular  Science  Monthly,  XIII.,  pp.  139- 
145,  4  figs.  The  Gigantic  Extinct  Armadillos  and  Their 
Peculiarities.  [Discusses  the  mechanical  genesis,  degen- 
eration, and  coalescence  of  vertebral  centra.] 

1885.  Ryder,  J.  A.  American  Naturalist,  pp.  411-415.  On  the 
Position  of  the  Yolk-Blastopore  as  Determined  by  the  Size 
of  the  Vitellus. 

1885.  Ryder,  J.  A.  American  Naturalist,  pp.  8i5-8"i9  and  903- 
907.  On  the  Availability  of  Embryological  Characters  in 
the  Classification  of  the  Chordata. 

1885.  Ryder,  J.  A.  American  Naturalist,  pp.  1013-1016.  On  the 
Genesis  of  the  Extra  Terminal  Phalanges  in  the  Cetacea. 

1885.  Ryder,  J.  A.     American  Naturalist,  pp.  90-97.     An  Outline 

of  a  Theory  of  the  Development  of  the  Unpaired  Fins  of 
Fishes. 

1886.  Ryder,  J.  A.     American  Naturalist,  pp.  179-185.  The  Origin 

of  the  Amnion. 


530    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 

1886.  Ryder,  J.  A.     Annual  Report  U.  S.  Commissioner  of  Fish 

and  Fisheries  for  1884,  pp.  981-1085,  PI.   IX.     On  the 
Origin  of  Heterocercy,  etc. 

1887.  Ryder,  J.  A.     American  Naturalist,  pp.  780-784.     A  Theory 

of  the  Origin  of  Placental  Types,  etc. 

1887.  Cope,    E.    D.     American  Naturalist,   pp.   985,    1060.     The 

Perissodactyla. 

1888.  Cope,  E.  D.     Proceedings  of  the  American  Association  for 

the  Advancement  of  Science,  p.  254.    On  the  Mechanical 

Origin  of  the  Sectorial  Teeth  of  the  Carnivora. 
1888.  Cope,  E.  D.     American  Naturalist,  p.  3.     The  Mechanical 

Causes  of  the  Origin  of  the  Dentition  of  the  Rodentia. 
1888.  Cope,  E.   D.     Proceedings  of  the  American  Philosophical 

Society,  p.  80.     The  Mechanical  Origin  of  the  Dentition 

of  the  Amblypoda. 

1888.  Ryder,   J.  A.     American  Naturalist,  p.    547.     The  Several 

Functions  of  the  Enamel  Organ  in  the  Development  of  the 
Teeth  of  Mammals,  and  on  the  Inheritance  of  Mutilations. 

1889.  Cope,  E.  D.     American  Naturalist,  March.     The  Artiodac- 

tyla.     (The  elbow-joint ;  the  zygapophyses.) 

1889.  Cope,  E.  D.  American  Journal  of  Morphology,  III.,  p.  137. 
The  Mechanical  Causes  of  the  Development  of  the  Hard 
Parts  of  the  Mammalia. 

1889.  Hyatt,  A.  Smithsonian  Contributions  to  Knowledge,  and 
Memoirs  of  the  Museum  of  Comparative  Zoology,  Cam- 
bridge, XVI.,  No.  3.  The  Genesis  of  the  Arietidae. 

1889.  Dall,  W.  H.  American  Journal  Science  and  Arts,  XXXVIII., 
p.  445.  Hinge  of  Pelecypoda  and  Its  Development. 

1889.  Osborn,  H.  F.  Transactions  American  Philosophical  So- 
ciety, XVI.,  p.  531.  (Published  February,  1890.)  The 
Evolution  of  the  Ungulate  Foot ;  The  Mammalia  of  the 
Uinta  Formation. 

1889.  Ryder,  J.  A.  American  Naturalist,  pp.  218-221.  The  Po- 
lar Differentiation  of  Volvox,  etc. 

1889.  Ryder,  J.  A.    American  Naturalist,  pp.  271-274.  The  Quad- 

rate Placenta  of  Sciurus  hudsonius. 

1890.  Ryder,  J.  A.     Proceedings  American  Philosophical  Society, 

XXVIII.,  pp.  109-159.     The  Origin  of  Sex,  etc. 
1890.   Ryder,  J.  A.     American  Naturalist,  pp.  376-378.     The  Pla- 

centation  of  the  Hedgehog  and  Phylogeny  of  the  Placenta. 
1890.  Packard,  A.  S.     Proceedings  Boston  Society  Natural  His- 


THE  OPINIONS  OF  N-EO-LAMARCKIANS.       53i 

tory,  XXIV. ,  p.  493.     Hints  on  the  Evolution  of  Certain 

Bristles,  Spines,  and  Tubercles  of  Certain  Caterpillars. 
1890.  Dall,   W.   H.      Proceedings  of    the   Biological    Society   of 

Washington,  May.     On  Dynamic  Influence  in  Evolution. 
1890.  Jackson,  R.  T.     Memoirs  Boston  Society  Natural  History, 

IV.,   p.   277  (July);    American  Naturalist,    1891,   p.    n. 

Phylogeny  of  the  Pelecypoda  ;  The  Aviculidae  and  Their 

Allies. 

1890.  Dall,  W.  H.     Transactions  of  the  Wagner  Free  Institute  of 

Science,  Philadelphia,  III.,  p.  58  (September).  American 
Naturalist,  1894,  P-  9°9-  Origin  of  the  Plaits  on  Columella 
of  Gastropoda. 

1891.  Scott,  W.  B.     American  Journal  of   Morphology,   p.    378. 

On  the  Osteology  of  Mesohippus  and  Leptomeryx ;  On 
Some  of  the  Factors  in  the  Evolution  of  the  Mammalia. 

1891.  Ward,  Lester  F.     Proceedings  Biological  Society  of  Wash- 

ington, Annual  Address.  Nee-Darwinism  and  Neo-La- 
marckism. 

1892.  Elliot,  D.  G.     The  Auk,  IX  ,  January.     The  Inheritance  of 

Acquired  Characters. 

1892.  Ryder,  J.  A.  American  Naturalist,  pp.  923-929.  A  Geo- 
metrical Representation  of  the  Relative  Intensity  of  the 
Conflict  Between  Organisms. 

1892.  Ryder,  J.  A.  Proceedings  Academy  Natural  Sciences,  Phila- 

delphia, pp.  219-224.  On  the  Mechanical  Genesis  of  the 
Scales  of  Fishes. 

1893.  Sharp,  Benj.     American  Naturalist  (February),  p.  89.  Joint 

Formation  Among  the  Invertebrata. 

1893.  Ryder,  J.  A.  Proceedings  American  Philosophical  Society, 
p.  192.  Energy  as  a  Factor  in  Organic  Evolution. 

1893.  Hyatt,  Alpheus.  Proceedings  Boston  Society  Natural  His- 
tory, p.  59.  Bioplastology  and  the  Related  Branches  of 
Biologic  Research. 

1893.  Riley,  C.  V.  Proceedings  Entomological  Society  Washing- 
ton, II.,  June,  No.  4.  Parasitism  in  Insects. 

1893.  Orr,  Henry  B.  A  Theory  of  Development  and  Heredity. 
New  York  and  London  :  Macmillan  &  Co.  8vo.  pp.  255. 

1993.  Hyatt  Alpheus.  Proceedings  of  the  American  Philosophical 
Society,  p.  349.  The  Phylogeny  of  an  Acquired  Charac- 
teristic. 


532    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION, 

1894.  Ryder,  J.  A.     American  Naturalist,  p.  154.     Orr's  Theory 

of  Development  and  Heredity. 
1894.  Cope,  E.  D.     American  Naturalist,  p.  205.     The  Energy  of 

Evolution. 
1894.  Cope,  E.  D.     New  Occasions,  No.  6  (May),  Chicago.     The 

Origin  of  Structural  Variations. 
1894.  Scott,  W.  B.     American  Journal  Science  and  Arts,  XLVIII. 

p.  355.     Mutation  and  Variation. 


INDEX. 


Abnormal  articulations,  275. 
Abortion  of  phalanges  in  ungulates, 

353- 

Acanthodeans,  92. 
Acanthopterygia,    102,  103,    104,    105, 

108, 

Acceleration,  9,  201. 
Acquired  characters,  10,  399,  401,  402, 

458. 

Acrania,  87,  94,  95,  193- 
Acris,  71. 

Actinopterygia,  100,  172. 
Actinozoa,  82,  83. 
Adapidae,  155. 
Adirondacks,  50. 
sElurodon  strvus  Leidy,  342. 
^Ethalium,  503. 
^Etheria,  267. 
Affections,  517. 

Africa,  73,  88,  115,  163,  168,  462. 
Agamidae,  73. 
Agassiz,  A.,  172,  175. 
Agel&us  phaniceus,  52. 
Ageniosus,  103. 
Aglossa,  63. 
Agnatha,  99,  195. 
Alaska,  49,  50. 
Algae,  75,  77. 

Allen,  H.  Dr.,  47,  302,  334,  357. 
Allen.  J.  A.,45- 
Altruism,  517. 
Amblypoda,  128,  132,  133,  141,  143,  144, 

297,  34i.  354.  520. 
Amblyrhiza,  352. 

Amblystoma  tigrinuni,  58,  59,  200. 
Amblystomidae,  58,  199. 
Ameghino,  154,  157,  357,  365. 
America,  426. 


Ametabola,  203.  ** 
Ammocoetes,  204. 
Ammonitinae,  187,  188,  189,  190 
Ammonoids,  187,  188,  422. 
Ammonoidea,  421. 
Amoeba,  76,  249. 
Amcebodect  mastication,  318. 
Amphignathodontidae,  71. 

Amphimixis,  459 — • 

Amphioxus,  86,  457. 
Amphisilidae,  104. 
Amphiuma,  113,  218. 
Anabolism,  481.- — 
Anacanthini,  105,  106. 
Anagenesis,  202,  475,  479,  516.  ~~ 
Anaplasis,  201.  . — - 
Anaptomorphus,  155. 
Anaptomorphidae,  154. 
Anarcestes,  187. 
Anchitherium,  148,  320,  359. 
Ancistrodon  contortrix,  22. 
Ancyloceras,  189. 
Ancylopoda,  128,  140,  143. 
Anelytropidae,  123. 
Anguidae,  123. 
Annelides,  269. 
Anniellidae,  123. 
Anodonta,  261. 
Anomia,  170,  177. 
Anontia  glabra,  265. 
Anomodontia,  115. 
Anthropomorpha,   132,   133,  143,  154, 

157.  158,  159,  305- 
Antichemism,  484.  «---~" 
Antilocapra  amerzcana,  55. 
Ants,  462,  500. 
Anura,  107,  no,  in,  113. 
Aphrododiridae,  104. 


534    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


Appendicularidae,  87. 
-Archaesthetism,  505,  513. 
Archean  beds,  83. 
Archeopteryx,  124. 
Archipterygium,  91. 
Archosauria,  114. 

Arcifera,  64,  65,  70,  71,  196,  197,  389. 
Arctic  Region,  52. 
Argentina,  357. 
Arietidae,  189. 
Artemia,  229,  230,  466. 
Artemia  salina,  229 ;  A.  muelhausenii, 

229. 
Arthropoda,  80,  81,  82,  83  172,  250,  253, 

268.  269,  368,  369,  389,  391,  404. 
Articulations,  of  Arthropoda,  269  ;  of 

Vertebrata,  275,  287. 
Artiodactyla,  69,  132,  133,  150, 195,  248, 

295.  296,  312,  313,  3H,  315.  3i8,  320, 

325,  359.  36o.  36i,  520. 
Arvicola,  349,  351. 
Aryan,  159. 
Asia,  73. 

Aspergillum,  265. 
Astacus,  hand  of,  274. 
Atrophy,  of  incisor  teeth,  356 ;  of  the 

ulna  and  fibula,  355. 
Australia,  72. 
Australians,  163,  166. 
Austroriparian,  29. 
Avian  line,  123. 
Axis,  196,  199. 
Axolotl,  58. 

Bactrites,  187. 

Baculites,  189,  190. 

Bain,   494. 

Baird,  S.  F.,  47. 

Baker,  F.  Dr.,  469. 

Balcena  mysticetus,  353. 

Ball,  W.  P.,  461,  465,  466. 

Barber,  M.  E.,  231,  234. 

Barrande,  185. 

Barrandeoceras,  413. 

Batavia,  168. 

Bather,  192. 
•  Bathmic  energy,  480. 
_Bathmism,  449,  479,  484. 
.Bathmogenesis,  484,  486. 

Bathyergus,  349. 

Batrachia,  87,  88,  89,  91,  94,  95,  97,  98, 


108,  115,  116,  121,  172,  193,  195,  196, 
218,  253,  363,  364,  365,  368,  372,  388. 

Batrachia,  line  of  the,  108;  respira- 
tion of,  93,  193  ;  remains  of,  no;  B. 
salentia,  8,  63,  69,  70,  314,  389 ;  B.  uro- 
dela,  314.  367. 

Batrachidae,  107. 

Baur,  G.  115,  366. 

Bear,  21. 

Beauchamp,  500. 

Beard,  Dr.  85. 

Beaume,  229. 

Beddard,  F.  E.,  238,  240,  292. 

Beecher,  C.  E-,  10,  176,  191. 

Bees,  463,  465. 

Belt,  500. 

Berthollet,  483. 

Bioplastology,  192.  ~^ 

Blastocerus,  196. 

Blastomeryx,  317. 

Blindness  of  cave  animals,  241. 

Boa  constrictor,  122. 

Bo6idea,  328. 

Bos,  144  ;  B,  taurus,  22, 

Bouchardia,  178,  179. 

Bovidae,  69,  209,  313,  315,  317. 

Brachiopoda,  191. 

Brachiopodus  Mollusca,  58. 

Bradypus,  313. 

Bragg,  C.  L.  244. 

Brain,  vertebrate — development  of 
94. 

Branchinecta  ferox,  230 ;  B.  media, 
230 ;  B.  scheefferii,  230 ;  B.  spinosa, 
230. 

Branchiostoma,  86,  92. 

Branco,  188 

Brazil,  462. 

Breeding,  422,  437. 

Brehm,  301. 

Brevicipitidae,  70. 

Brewer,  W.  H.,  422,  426,  430,  431,  435, 

437- 

Bridger,  139. 
Brinton,  468. 
British  America,  49. 
Brooks,  86,  454,  459. 
Brown,  A.,  189,  190. 
Brown-Sequard,  430. 
Brunn,  A.  von,  403,  446. 
Buccinum,  260. 


INDEX. 


535 


Buckman,  J.,  23,  189,  228. 
Bufonidae,  65,  70,  189,  199,  389. 
Bumpus,  H.  C.,  242. 
Bunotheria,  127,  132,  133.  14°,  141.  H5- 
Bushmen,  159. 

Butterfly,  peacock,  232;  B.,  swallow- 
tailed,  231 ;  B.,  tortoise  shell,  232. 

Caeciliidae,  113,  218. 

Ctenoceras  aratum,  417 ;   C.  clausam, 

417 ;  C.  intermedium,  417 ;  C.  linea- 

tum,  417. 

•Caenogeny,  200,  209. 
Calamodon,  330. 
California,  50. 
Callianassa,  273. 
Callianassa  stimpsonii,  242,  273. 
Calyptocephalus  gayi  D.  and  B.,  68. 
Cambarus    bartonii,    241 ;   C.    setonii, 

241. 

Cambrian,  beds,  83;  time,  176. 
Camelidae,  69. 
Canidae,  48,  49,  59,  339,  342- 
Canis,  21,  59;  latrans,  48;  lupus,  48. 
Caprimulgidae,  126. 
Carbonic,  epoch,  99,  101,  108,  184,  188, 

416,  417,  418,  419,  420;  beds,  77,  363. 
Cardium,  261. 
Cariacus,  196. 
Carnivora,  48,  50,  127,   132,   133,  135, 

140,  143,  144,  293,  302,  305,  309,  318, 

322,  330,  335,  34°,  343.  346,  360,  361, 

379,  388,  519- 
Carpophyta,  77. 
Carriere,  M.,  227. 
Carter,  H.  J.,  504. 
Gary,  377,  378,  379,  380,  381,  402. 
Cassina,  71. 
Castor,  351. 

Castoroides,  330,  349,  351. 
Castoroides  ohioensis,  347,  350. 
•  Catagenesis,  202,  211,  475,  479,  516. 
-Cataplasis,  202. 
Caterpillars,  230,  525. 
Causes  of  Variations,  223. 
Cave  animals,  241,  521. 
Cavia,  348. 
Caviidae,  351,  352. 
Cebidae,  155. 

Cebus  apella,  500 ;    C.  capucinus,  500. 
Cell-division,  489. 


Cells,  germ,  447,  480;  glandular,  440; 
muscle,  249 ;  nerve,  450, 453 ;  repro- 
ductive, 446,  453  ;  somatic,  453,  456. 

Cenogenesis,  200. ~ 

Cenozoic,  304,  357,  419,  420. 

Centetes,  335. 

Centetidae,  145,  335. 

Central  America,  29,  49,  52. 

Cenrtrina,  53,  68,  388. 

Cephalopoda,  8,  182,  183,  192,  218,  405, 
408,  520. 

Ceratobatrachidae,  71. 

Ceratophrys,  71. 

Cercopithecidae,  469. 

Cervidae,  51,  69,  196,  315,  317. 

Cervus,  196,  312. 

Cervus  canadensis,  297  ;  elaphus,  298. 

Cetacea,  127, 138, 140,  142,  143,  145,  155, 
268,  303,  304,  352,  353,  355,  374- 

Chabry,  458. 

Chaetodontidae,  107. 

Cham  a,  267. 

Characiniidae,  103. 

Chelmo,  107. 

Chelydobatrachus  gouldii  Gray,  68. 

!    Chemism,  484.. 

I    Chilonyx,  117. 

Chimpanzee,  elbow-joint  of,  295. 

Chinchillidae,  351,  352. 

Chirogidae,  324. 

Chiroptera,  127,  132,  143,  336,  358. 

Chiropterygium,  91. 

Chirox,  325. 

Chlorophyll,  75. 

Choloepus,  313. 

Chondrioderma  difforme>  220. 

Chondrotus  tenebrosus,  58,  59. 

Chordata,  86,  205,  215,  218. 

Chorology,  387. 

Chrysochloridae,  335. 

Chrysochloris,  310. 

Cicindela,  variations  in,  25. 

Ciona  intestinalis,  456. 

Cladodus,  100. 

Clarke,  176,  191. 

Claus, 211. 

Clepsydropidae,  319. 

Climatius,  92. 

Cnemidophorus,  199 ;  color-variation 
of,  41. 

Cnemidophorus   deppei,   41 ;    C.    gra- 


536    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


hamii,  46;  C.  gularis,  41,  46,  200;  C. 
costatus,  46;  C.  scalar  is,  46,  200  ;  C. 
semifasciatus,  43,  46 ;  C.  mariarunt, 
41,  45 ;  C.  sexlineatus,  41,  46 ;  C.  ter- 
sellatus,  41,  46;  C.  melanostethus, 
46 ;  C".  perplexus,  46 ;  C.  rubidus,  45, 
46 ;  C.  septemvittatus,  46 ;  C.  vario- 
losus,  46. 

Coassus,  196. 

Cobitis,  363. 

Cobra  de  capello,  22. 

Coelacanthidae,  gi. 

Cceleoterata,  79,  81,  82,  83,  250. 

Coelogasteroceras  canaliculatum,  421. 

Cohesion,  484. 

Colaptes  auratus,  52. 

Coleoptera,  203. 

Colocephali,  104,  106. 

Coloceras  globatunt,  4,  16. 

Color  changes,  in  Lepidoptera,  230; 
in  cocoons,  440;  in  birds,  238:  in 
fishes,  499;  in  tree-frogs,  499. 

Color  variations,  in  the  genus  Cicin- 
dela,  25  ;  in  Osceola  doliata,  29 ;  in 
Cnemidophorus,  41. 

Colostethidae,  78. 

Columba  livia,  21. 

^-—Complementary  growth-energy,  248. 
—  Conditions  of  inheritance,  438. 

Condylarthra,  84,  85,  132,  133,  134, 135, 
141,  143,  157,  356,  357.  359,  388. 

Coniferae,  77. 
..^-Conscious  energy,  507. 

Consciousness,  495,  505. 

Consciousness  and  automatism,  495. 

Conversion  of  Artemia  into  Branchi- 
ata,  229. 

Cope,  E.  D.,  8,  528. 

Copepoda,  211. 

Cophylidae,  70. 

Copperhead,  22. 

Corvus  amerzcanus,  52. 

Coryphodon,  354. 

Coryphodontidae,  318. 

Cosoryx,  315,  317. 

Cosoryxfurcatus,  315  ;  C.  necatus,  315; 
C.  ramosus,  315  ;  C.  teres,  315. 

Cossus  ligniperda,  237. 

Costa  Rica,  50. 

Cotylosauria,  87,  88,  113,  115,  122,  172. 

Crangon,  hand  of,  274. 


Craniomi,  100. 

Creodonta,  336,  337,  338,  339,  341,  343, 

388. 
Cretaceous,  139,  143,  184, 189,  419,  420, 

421,  422. 

Cricotus  crassidiscus,  HI. 
Crioceras,  189. 
Crocodilia,  94,  114,  116. 
Crocuta  ntaculata,  294. 
Crossopterygia,  100,  101. 
Crotalus  horridus,  22. 
Crustacea,  211,  271,  273. 
Cryptopnoy,  494. 
Ctenophora,  272. 
Ctetology,  192. 
Cunningham,  J.  L.,  238,  527. 
Cyanurus  cristatus,  52. 
Cyclops,  212. 
Cyclopterus,  108. 
Cycloturus,  314. 
Cymatoceras  elegans,  418. 
Cynodictis  geismarianus,  341. 
Cynognathidae,  88. 
Cypraea,  260. 
Cypraeidae,  261. 
Cyprinidae,  103. 
Cyrtoceras,  185,  408,  413. 
Cystignathidae,  65,  70,  71. 
Cystignathus  pachypus,  390. 

Dall.  W.  H.,  10,  58,  255,  520,  530,  531. 

Dama,  196. 

Darwin,  C.,  3,  4,  5,  6,  7,  14,  231,  247, 

248,  249,  385,  387,  398,  474,  48o. 
Darwin,  E.,  10,  505. 
Daubentonioidea,  128. 
Degeneracy,  247;    in  birds,  126;    in 

plants,  76 ;  in  reptiles,  122 ;  in  crus- 

tacea,  211 ;    in  mollusca,   213;    in 

vertebrata,  215. 
Delphinidae,  303. 
Deltatheriutn  fundaminis,  335. 
Dendrobatidae,  70. 
Dendrophryniscidae,  70. 
Dentition  modification,  in  Canidae, 

59 ;  in  Felidae,  60 ;  in  Homo,  60,  61 ; 

in  lemurs,  61 ;   in  lower  placenta! 

mammals,  61 ;  in  monkeys,  61. 
Depuy,  430. 
Dercetidae,  104. 
'    Descartes,  498. 


INDEX. 


537 


Designed  action  in  animals,  500. 
Devonic  period,  77,  91,  101,  172,  184, 

186,  188,  362,  415,  420,  422. 
Diadectidae,  89. 
Diadiaphorus,  359. 
Dibamidae,  123. 
Dicrocerus,  315. 
Didelphodus,  335. 
Didymium  squamulosum,  220. 
Digits,  number  of,  309. 
Dimorphodon,  120. 
Dimya,  267. 

Dinocerata,  314,  315,  356. 
Dinosauria,  98,  114,  116,  120,  121,  122, 

304,  372. 

Dioplotherium,  330. 
Diplarthra,  84,  128,  133,  136,  143,  144, 

146,  293,  295,  297,  300,  302,  305,  306, 

312,  313,  320,  332,  360,  403- 
Diplogenesis,  12,  441,  443,  470. 
Dipneusta,  89. 
Dipnoi,  89,  99. 
Diprodontidae,  143. 
Diptera,  203,  204. 
Dipus,  361. 
Disciniscus,  177. 
Dissacus,  302. 
Disuse  in  Mammalia,  352. 
Dog-opossum,  22. 
Dohrn,  204. 

Dolichotis,  361 ;  D.  patachonica,  305. 
Dollo,  121. 
Domestic  fowls,  21. 
D'Orbigny,  417. 
Dorypterus,  103. 
Driesch,  457. 

DuBois,  Dr.,  159,  168,  169. 
Dume"ril,  58. 

Dynamical  evolution,  524. 
Dyscophidae,  70. 
Dysodus,  59,  146. 

Echidermata,  368. 

Echinodermata,  80,  81,  82,  83. 

Echinus,  457. 

Ectal  mastication,  318. 

Edaphoceras,  186. 

Edentata,  127,  132,  133,  138,  141,  143, 

145, 186,  195,  303,  305,  310,  356,  360. 
Education,  505. 
Eels,  103. 


Effect  of  feeding  on  color  in  birds, 
238. 

Effect  of  light  on  the  colors  of  flat- 
fishes, 238. 

Effects  of  consciousness,  509. 

Efficient  cause,  10,  497,  498. 

Eigenmann,  C-,  244. 

Eimer,  23,  45,  252,  254,  527. 

Elasmobranchii,  91,  94,  95,  99. 

Elasmotherium,  314. 

Elbow-joint,  of  Cervus  elaphus,  296; 
of  chimpanzee,  295 ;  of  horse,  ab- 
normal, 278 ;  human,  abnormal, 277. 

Elephas,  145,  330. 

Elliot,  D.  G.,  531. 

Elosia  nasus  Licht,  68. 

Embolomeri,  88,  109,  uc. 

Embryology,  202,  209,  401. 

Embryonic  variations,  444. 

Emphytogenesis,  486. 

Endoceras,  186. 

Endolobus,  186;  E.  excavatum,  417. 

Energies,  specific,  480. 

Energy,  448,  451,  506,  507,  512;  synop- 
tic table  of,  484;  anagenetic,  478, 
484 ;  definition  of,  473 ;  of  evolu- 
tion, 473 ;  catagenetic,  479,  484 ;  cor- 
relation of,  506 ;  inorganic,  475,  484, 
512  :  composition  of,  490. 

Engystomidae,  70. 

Enhydra,  352. 

Ental  mastication,  318. 

Entoconcha  mirabilis,  213. 

Environment,  physical  influences  of, 
436,  452,  475. 

Eocene,  61,  104,  135,  138,  139,  142,  143, 
145,  147,  150,  154,  155,  173,  205,  304- 
365,  377- 

Epigenesis,  13. 

Epihippus,  147,  148. 

Epilasmia,  107. 

Epilepsy  in  Cavia,  430. 

Equidae,  313. 

Equilibrium,  508.  . 

Equus,  145,  149,  359 ;  E.  caballus^  84, 
300. 

Ergogenesis,  486. 

Erinaceus,   127. 

Erismatopterus,  104. 

Eryops  megacepalus,  371. 

Esquimaux,  61,  153. 


538    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


Esthonyx,  329. 
Eudoceratidae,  186. 
Euprotogonia,  147. 
Europe,  55,  160,  426,  427. 
Europeans,  166. 
Europeo-Americans,  153. 
Eurypharyngidae,  104. 
Eusophus  nebulosus  Gir,  68. 
Eusthenopteronfoordii,  91. 
Eutaenia,  63  ;  E.  saurtta,  21;  E.  sirta- 

lis,  21,  63. 
Eutheria,  373. 
Evolution,  science  of,  22. 
Expression  points,  25. 

Faxoe,  418. 

Feet  of  Chinese  women,  399. 

Felidae,  48,  49,  145,  342. 

Felis,  339. 

Felis  concolor,  49 ;    F.  dontestzca,  21  ; 

F.  pardalis,  50. 
Fellahs,  163. 
Ferns,  77. 

Pick,  R.,  283,  284,  286,  377,  528. 
Firmisternia,  64,  70,  71,  196,  197,  389, 

390. 

Fisher,  91,  99,  101,  104. 
Fishes,  ancestral  type  of,  86,  91,  99. 
Fistularia,  104. 
Flatfishes,  238. 
Flexure,  368. 
Florida,  52,  56. 
Flossensaum,  243. 
Forel,  463. 

Forsyth-Major,  334,  469. 
Fraipont,  160,  161,  165,  166,  170. 
France,  83,  170,  315. 
Friction,  279,  519,  378,  490. 
Fuligo,  503. 

Functions  of  consciousness,  495. 
Fungi,  70,  219. 
Furcifer,  197. 
Fttsus  parilis,  257. 

Gage,  363. 
Galeopithecus,  328. 
Gallinae,  391. 
Gallus  sp.,  21. 
Galton,  Dr.,  12,  471. 
Ganocephali,  no. 
Garman,  S.,  241. 


Garter-snake,  21. 

Gasterosteidae,  104. 

Gastraea  theory,  202. 

Gastrechmia,  63. 

Gastropoda,  plaits  in  shell  of,  255. 

Gazella  dorcas,  301. 

Gebia,  273. 

Gecconidae,  73,  88,  122. 

Gegenbaur,  91,  366. 

Gelocus,  312. 

Genealogy,  of  man,  171 ;  of  the  horse, 

146. 

Genesiology,  192. 
Geomyidae,  352. 
Giard,  527. 
Glauconiidae,  121. 
Gleditschia,  228. 
Glires,  51,  127,  132,  133,  135.  HI.  *43, 

305.  3i8,  324,  328,  329,  330,  331,  334. 

345.  346,  360,  361,  404- 
Glochidia,  203. 
Glossophaga,  328. 
Glossophaginae,  356. 
Gloxinia,  384. 
Glyptodontidae,  303. 
Gobius,  499. 
Goethe,  247. 

Gonagenic  variations,  444. 
Goniatitinae,  186,  187,  188,  422. 
Gravitation,  484. 
Growth-energy,  449,  473 ;  G.  force, 

484. 

Gulick,  388. 
Gulo  luscus,  50. 
Gunther,  123,  390. 
Gwynia,  178,  179. 
Gymnosperms,  79. 
Gyroceras,  185. 

Haeckel,  E.,  7,  8,  85,  88,  89,  154,  169, 

175,  201,  202,  387,  448,  454. 

Halicore,  330,  336. 
Hall,  176. 
Halloceras,  186. 
Hamites,  189. 
Hapalidae,  141. 
Haplodoci,  106,  107. 
Haplomi,  103,  104,  106. 
Harpa,  261. 

Hawaiian  Islands,  388. 
Heliotropism,  503. 


INDEX. 


539 


Hemibranchii,  104,  106. 

Hemimantis,  71. 

Hemiphractidae,  71. 

Henke,  277,  283,  528. 

Henslow,  G.,  23,  226,  227,  228,  383,  384, 
527- 

Herdman,  215. 

Heredity,  398. 

Hering,  492. 

Hertwig,  456,  457. 

Hesperornithidae,  124. 

Heteroglossa,  71. 

Heterologous  series,  71. 

Heteromorphosis,  455. 

Heterosomata,  105,  106. 

Hilgard,  S.  W.,  433. 

Hinnites,  267. 

Hippocampidae,  105. 

Hippopotamidae,  69. 

Hippopotamus,  330,  402. 

Hippotherium,  84,  149,  359 ;  H.  medi- 
terraneum^  84. 

H6ffding,498. 

Holocephali,  99. 

Holoptychiidae,  91. 

Holostei,  101,  102. 

Holostomi,  106. 

Hominidae,  157. 

Homo,  155,  158,  169,  170. 

Homogeneous  series,  71. 

Homogeny,  72. 

Homologous,  series,  71. 

Homology,  19. 

Homo  neanderthalenszs,  170;  H.  sa- 
piens, 170 ;  H.  erectus,  169. 

Homoplassy  in  Mammalia,  72,  357. 

Homoplastic  series,  71. 

Hoplobatrachus,  71. 

Horn,  G.  H.,  25,  29. 

Horns,  314  ;  of  Cervus  elaphus,  197. 

Horse,  evolution  of  trotting,  426;  H. 
phylogeny  of,  146,  522. 

House-fly,  254. 

Hunger,  '504. 

Hurst,  C.  H.,  205,  207. 

Huter,  251,  275.  276,  331. 

Huxley,  89,  99,  476. 

Hyaenidae,  145,  342,  343. 

Hyaenodon,  343. 

Hyatt,  A.,  8,  9,  10,  175,  182,  183,  201, 


202,  266,  268,  405,  420,  451,  520,  528, 
529,  530,  531- 

Hybodus,  372. 

Hybopsis  biguttatus,  22. 

Hydroids,  82. 

Hydrotropism,  501. 

Hyla,  ii,  198, 199  ;  H . carolinensis,  499; 
H.  gratiosa,  499. 

Hylella,  71,  198,  199. 

Hylidae,  65,  70,  198. 

Hylobates,  159. 

Hymen,  399. 

Hymenoptera,  82,  903. 

Hyopotamus,  312. 

Hyperolius,  71. 

Hypothesis  of  the  origin  of  the  divi- 
sions of  the  Vertebrata,  362. 

Hypsiboas  donmercii  D.  and  B.,  68; 
H.  punctatus  Schu.,  68. 

Hyracoidea,  132,  133,  141,  143.  332. 

Hyracotheriinae,  313. 

Hyracotherium,  147,  148,  302. 

Hystricidae,  351. 

Ibacus,  274. 

Ichthyocephali,  106. 

Ichthyopterygia,  113,  116,  121. 

Ichthyornithidae,  124. 

Ichthyosaurus,  121. 

Ichthyotomi,  100. 

Icichthys,  108. 

Icosteus,  108. 

Iguanidae,  73. 

Impact,  277,  284,  287,  291,  302,  305,  311, 
485- 

Impressed  zone  of  the  nautiloids,  405. 

Increase  of  size  through  use,  304. 

India,  159. 

Indo-Europeans,  153. 

Inexact  parallelism,  200. 

Influence,  of  external  stimulus  on  mo- 
tions of  animals,  496 ;  of  the  mental 
condition  of  the  mother  on  the  fos- 
tus,  434,  451 ;  of  mind  on  coloration, 
499;  of  mind  on  matter,  498. 

Infusoria,  79,  511. 

Inheritance,  of  acquired  characters, 
401,  405  ;  of  characters  due  to  dis- 
ease, 430;  conditions  of  438,  440, 
of  exercise  of  function,  426;  of  mu- 


540    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


tilation  and  injuries,  399,  431  ;  of 
nutrition,  423;  of  regional  influ- 
ences, 435,  440. 

Insecta,  213,  226. 

Insectivora,  136,  140,  143,  305,  332,  336, 
361. 

Intelligence,  animal,  500,  504. 

Introduction,  i. 

Ischyromystypus,  Leidy,  351. 

Ismenia,  178,  179. 

Isolation,  387. 

Isospondyli,  103,  106. 

Jackson,  R.  T.,  10,  191,  261,  520,  531. 
Jaeger,  10. 

Japanese  spaniel,  60. 
Java,  160. 
Java  man,  169. 
Jayne,  H.  Dr.,  60. 
Jordan,  Dr.,  101. 
Joseph,  Dr.,  242. 
Judgment,  504,  506. 
Juglans  m'gra,  466;  J.  regia,  466. 
Jura,  122,  139,  140,  142,  143,  184,   188, 
417,  418,  419,  420,  421. 

Katabolism,  481. 

Kinetobathmism,  485. 

Kinetogenesis,  225,  246,  287,  375,  496 ; 
in  Mammalia,  288 ;  in  Mollusca, 
255;  of  muscle,  249;  objections  to 
the  theory  of,  375  ;  of  osseous  tis- 
sue, 275  ;  under  impact  and  strain, 
519;  under  use  in  Vermes  and  Ar- 
thropoda,  268 ;  in  Vertebrata,  275. 

Kingsley,  J.  S.,  89,  213. 

Koelliker,  Dr.,  285,  331,  377,  381. 

Kowalevsky,  323. 

Kukenthal,  333. 

Lacerta  muralis,  45,  195;  L.  m.  albi- 
ventrtS)  46 ;  L.  m.  campestris,  46 ;  L. 
m.  maculostrz'ata,  46;  L.  m.  punctu- 
latofasciata,  46 ;  L.  nt.  reticulata, 
46 ;  L.  nt.  strzatomaculata,  46  ;  L.  nt. 
tigrz's,  46. 

Lacertilia,  88,  116,  120,  121,  122,  123, 
218,  314,  372. 

Lamarck,  2.  5,  7,  8,  12,  14,  241,  387, 
497- 

Lamellibranchs,  261. 


Lankester,  E.  R.,  71,  113. 

Laramie,  139. 

Larvacea,  215. 

Law  of  the  unspecialized,  172. 

Law,  Prof.,  431. 

Lawrence,  426,  427. 

Laws  of  organic  evolution,  3. 

Laws  of  structural  relations,  19. 

Leidy,  Professor,  351. 

Lemur  collaris,  326. 

Lemuridae,  155,  328,  339,  356,  469. 

Lemuroids,  157. 

Lemurs,  61,  150,  154,  155,  156. 

Leperditia,  262. 

Lepidoptera,  203,  204,  237,  440,  441. 

Leporidae,  348. 

Leptodactylus  pentadactylus,  Laur., 

390. 

Lepus,  351,  361  ;  L.  sylvaticus,  53. 
LerntEa.  branchialis,  212. 
Lernaeapoda,  212. 
Lesshaft,  277. 
Lifege,  160. 

Life,  definition  of,  513. 
Light  effect,  of,  on  flatfishes,  238. 
Lima,  266. 
Limbs,  moulding  of  articulations  of, 

287;  vertebrate  segmentation  01,367. 
Line  of  the  pisces,  99. 
Lingula,  176,  177. 
Liocephalus,  391. 
Liopeplum,  260. 
List  of  papers  by  American  authors 

on  the  law  of  kinetogenesis,  528. 
Litopterna,  357,  359. 
Lituites,  414 
Loeb,  455. 

Lohest,  160,  161,  165,  166,  168,  170. 
Lophiodontidae,  355. 
Lophobranchii,  105,  106. 
Louisiana,  50. 
Loup  fork,  139,  148,  315. 
Lucius  estor,   21  ;   L.  nobilior,  21  ;  L. 

vermzculatus,  21. 
Lytoceratinae,  190. 

Macacus,  391. 
Machrauchenia,  359. 
Mackenzie  River,  50. 
Magas,  178,  179. 
Magasella,  179. 


INDEX. 


Magellania,  178,  179. 

Magosphaera,  102, 

Malacopterygia,  102,  103,  104. 

Mammalia,  characters  of,  93 ;  line 
of  the  successional  modifications  of 
the  feet  and  digits  of,  133 ;  verte- 
brae of,  135  ;  dentition  of,  135 ;  phy- 
logeny  of,  138  ;  origin  of,  87;  brain 
and  nervous  system  of,  144. 

Man  of  Spy,  161. 

Maori,  168. 

Marey,  491. 

Marseniidae,  261. 

Marsh,  122,  123,  156,  174,  304. 

Marsipobranchs,  94,  95,  192,   193,  204. 

Marsupialia,  127,  132,  138,  142,  143, 
157,  305,  309,  336,  361,  374- 

Mastodonsaurus,  117. 

Maupas,  79,  459. 

Mead,  T.  H.,  31. 

Mechanical,  causes  of  dental  modifi- 
cations, 319  ;  conditions  of  segmen- 
tation in  Arthropoda,  269;  origin 
of  characters  in  Pelecypoda,  261  ; 
origin  of  the  impressed  zone  in 
Cephalopoda,  261. 

Megerlina,  178,  179. 

Melanesians,  154. 

Meldola,  Prof.,  231,  234. 

Meleagris  ga  Hop  a  vo,  21. 

Meniscoessus  conquzstus,  325. 

Meniscotherium,  156. 

Menodontidae,  355. 

Mental,  evolution,  510  ;  degeneracy, 
509;  processes,  506. 

Menuridae,  126. 

Merospondyli,  106,  372. 

Merrifield,  230. 

Merychoch&rus  montanus,  307. 

Mesohippus,  148. 

Mesonyx,  141,  302. 

Mesozoic  age,  79,  116,  188,  413. 

Metabolism,  481. 

Metaplasis,  202. 

Metatoceras  cavatifortne,  406;  M.  du- 
biitm,  408. 

Metazoa,  252. 

Mexico,  29,  48,  49,  388. 

Michahelles,  242. 

Microsauria,  109,  no. 

Miles,  M.,  481. 


Milk-snake,  29. 

Mind,  development  of,  364;  its  rela- 
tion to  matter,  507,  508. 

Mimetic  analogy,  392. 

Mimoceras,  187,  421. 

Minot,  C.  S.,  468. 

Miocene,  138,  139,  315. 

Mioclaenus,  335. 

Mississippi,  57. 

Mitchell,  Dr.  C.,  455. 

Mitra  lineolata,  259. 

Mivart,  154. 

Mixophyes,  71. 

Mnemogenesis,  492. 

Modiola,  264. 

Molar  teeth,  of  man,  61,  152;  of  Es- 
quimaux, 153  ;  of  Fan,  168 ;  of  man 
and  woman  of  Spy,  166 ;  of  Maori, 
168  ;  of  Tahitian,  168. 

Moll,  277. 

Mollusca,  8,  80,  81,  82,  83,  172,  182, 213, 
229,  254,  261,  368,  388,  523,  524. 

Moloch,  72. 

Monkeys,  intelligence  of,  500;  in 
Patagonia,  157. 

Monocondylia,  87,  372. 

Monodelphia,  132,  142,  144,  374. 

Monotremata,  88,  127,  132,  135,  138, 
140,  142,  143. 

Morphogeny  from  Gwynia  to  Dal- 
lina,  179. 

Morris,  C.,  363. 

Moschidae,  69. 

Moulding  of  the  articulations  in  the 
Vertebrata,  287. 

Mousterien  type,  170. 

MQhlfeldtia,  178,  179. 

Muller,  Aug.,  226,  383. 

Muller,  Johannes,  213. 

Mulleria,  265,  267. 

Multituberculata,  135,  145,  318,  324, 
325.  329.  388. 

Muscle,  kinetogenesis  of,  239;  striped, 
254. 

Mus  decumanus,  403. 

Mustela,  americana,  50 ;  M.  pennantt, 
50. 

Mustelidae,  342. 

Mutations,  222. 

Mutilata,  143,  288,  290,  291,  374. 

Mutilations,  398,  431. 


542    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


Mya  arenarta,  263,  265,  266. 
Mycetozoa,  219,  229. 
Myism,  484. 
Myrmecobius,  140. 
Myxomycetes,  75.  219,  501,  503. 

Nageli,  527,  528. 

Narwhale,  330. 

Natica,  213. 

Natural  selection,  247,  385,  474. 

Nature  of  variations,  113,  115. 

Naulette,  161,  162,  163,  165. 

Nautili,  183,  184,  185,  186,  408,  413,  417, 

418,  419,  420,  421,  422. 
Nautilinidae,  421. 
Nautiloids,  405,  415,  421. 
Neanderthal  man,  159,  161,  163,  165, 

169,  176. 
Necturus,  113. 
Negritos,  163,  166,  169,  154. 
Negro,  159,  163. 

Nematocarpa  filamentaria,  526. 
Nematognathi,  106. 
Neocaledonians,  163. 
Neocene,  143,  148. 
Neo-Darwinians,  381. 
Neo-Lamarckians,  255,   284,  375,  389, 

518. 

Neo-Lamarckism,  241,  518. 
Neolithic  man,  166. 
Neothyris,  178. 
Nephryticeras,  415. 
Neurism,  484,  496. 
Neuroptera,  203. 
New  Britain,  169. 
New  England,  49,  52,  56,  437. 
New  Granada,  29. 
Newton,  480. 
New  York,  50,  402,  437." 
Nigritos,  154,  163,  166,  169. 
Normal  articulations,  283. 
Norman  horse,  423. 
North  America,  10,  29,  47,  48,  53,  55, 

73,  115,  124. 
Nutrition,  423. 

Objections,  to  the  doctrine  of  inheri- 
tance of  acquired  characters,  458  ; 
to  kinetogenesis,  375  ;  to  the  doc- 
trine of  parallelism,  205. 

Obolella,  176. 


Odessa,  224. 

(Ecology,  v,  384. 

CEstridae,  102. 

Oliva,  260. 

Olivella,  260. 

Ononis  repens,  227 ;  O.  spinosa,  227 
228. 

Ontogeny,  444. 

OSphyta,  77. 

Opheontorphus  tnintus,  29. 

Ophidia,  116,  120,  122,  218,  372. 

Ophidioceras,  414. 

Opinions  of  Neo-Lamarckians,  518. 

Opisthobranchs,  261. 

Opisthotome  mastication,  318. 

Orbiculoidea,  177. 

Orconectes  pellucidus,  241. 

Ordovician,  77,  83,  176. 

Origin,  of  the  animal  line,  514;  of 
Batrachia,  89;  of  canine  teeth,  327; 
of  carnivorous  dentition,  332;  of  the 

'  dental  type  of  the  Glires,  345;  of 
divisions  of  the  vertebrates,  362 ;  of 
genera,  9 ;  of  the  plaits  in  the  col- 
umnella  of  the  gastropods,  255 ;  of 
plants,  514 ;  and  survival  of  the  fit- 
test, 4;  of  hereditary  individual 
variation,  n. 

Ornithosauria,  114,  120,  121. 

Ornithostomi,  143. 

Orr,  H.  B.,  531. 

Orthagoriscidae,  108. 

Orthal  mastication,  318. 

Orthoceras,  185,  187,  408. 

Orthognathism,  248. 

Orthoptera,  203. 

Ortyx  virginianus,  52. 

Osborn,  H.  F.,  152,  320,  324,  337,  378, 
379,  444,  470,  520,  521,  530. 

Osceola  doliata  annulata,  30,  35,  39; 
O.  d.  clerica,  31,  33,  39;  O.  d.  cocci 
nea,  30,  37,  39  ;  O.  d.  collaris,  31,  33, 
39 ;  O.  d.  conjuncta,  30,  39 ;  O.  d. 
doliata,  22,  29,  30,  33,  39 ;  O.  d.  gcn- 
tilis,  30,  37,  39 ;  O.  d.  parallela,  30, 
35,  39  I  O.  d.  polyzona,  30,  37,  39 ;  O. 
d.  syspila,  30,  35,  39 ;  O.  d.  tempora- 
h's,  3i  >  33.  391  O,  d.  triangula,  31, 
33,  39- 

Osteocephalus,  198,  199. 

Osteolepididae,  91. 


INDEX. 


543 


Ostraciontidae,  108. 

Ostracoda,  262. 

Ostrea,  261,  264,  265. 

Ostrea  edulis,  262 ;  O,  virginiana,  264. 

Ostreidae,  267. 

Otariidae,  353,  390. 

Otaspis,  199. 

Owen,  150. 

Oyster,  266,  267. 

Pacific,  29,  51,  56. 

Packard,  241,  521,  525,  530. 

Palaeomeryx,  196. 

Palaeoniscidae,  181. 

Palaeospondylus,  99. 

Palaeosyops,  377. 

Paleolithic,  flints,  170 ;  man,  169,  170  ; 

time,  160. 

Paleozoic,  188,  226,  413,  415,  417. 
Palinal  mastication,  318. 
Palingenesis,  200. 
Paludicola,  71. 
Pangenesis  theory,  of  Brooks,  454  ;  of 

Darwin,  450. 
Pantodonta,  141. 
Pantolambda,  141,  354. 
Pantotheria,  388. 
Pantylus,  117. 

Papilio  demoleus,  231 ;  P.  nz'reus,  231. 
Papuans,  163. 
Paradise-birds,  391. 
Parallelism,  20,  175 ;  in  the  Brachio- 

poda,  176  ;  in  the  Cephalopoda,  182  ; 

inexact,  200 ;  objections  to  doctrine 

of,  205  ;  in  the  Vertebrata,  192. 
Parasitism,  211,  214,  509. 
Pariotichus,  117. 
Parisians,  163. 
Passeres,  124. 
Patagonia,  157. 
Paterina,  176. 
Paurodon,  343. 
Pavlow,  M.,  84. 
Pea-fowls,  391. 
Pecten,  254,  264,  265,  266. 
Pediculati,  106. 
Pegasus,  104. 
Pelecypoda,  261. 
Pelobatidae,  70. 
Pelodytidae,  70. 
Peltaphryne  peltacephala  D.  &  B.,  68. 


Pelycosauria,  87,  88,  120,  172. 

Pennsylvania,  49,  437. 

Pepper,  Dr.,  278. 

Percomorphi,  104,  106,  108. 

Perigenesis,  448,  454. 

Periptychus,  141,  156,  268. 

Perissodactyla,  133,  312,  313,  318,  355, 
357,  359,  36o,  361,  390,  5i9- 

Permian,  87,  88,  98,  108,  no,  114,  115, 
121,  122,  172,  209,  218,  363. 

Perna,  264. 

Pernostrea,  267. 

Peropoda,  121. 

Perrier,  E. ,  527. 

Phacochoerus,  328. 

Phanerogamia,  77,  79. 

Pharyngognathi,  106,  107,  108. 

Phenacodontidae,  147,  150. 

Phenacodus,  146,  147,  156,  157,  205, 
302. 

Phenacodus  primcevits,  130,  137;  P. 
vortntanzz,  134. 

Phillipine  Islands,  166. 

Phocidae,  353. 

Phryniscidae,  70. 

Phrynocephalus,  73. 

Phrynosoma,  72. 

Phyllomedusa,  158. 

Phyllopod  Crustacea,  229. 

Phylogenetic  scheme  of  the  Mamma- 
lia, 127. 

Phylogeny,  general,  74,  444 ;  of  ani- 
mals, 79  ;  of  the  Batrachia,  108;  of 
the  birds,  123  ;  of  the  classes,  83 ;  of 
the  fishes,  99  ;  of  the  horse,  146 ;  of 
the  Mammalia,  126,  138;  of  man, 
150;  of  plants,  78;  of  the  reptiles, 
113 ;  of  the  Teleostomata,  101 ;  of 
the  Vertebrata,  83  ;  of  the  Actino- 
pterygia,  101. 

Physarum  leucophceum,  220. 

Physeteridae,  303. 

Physiobathmism,  485. 

Physiogenesis,  225,  227,  435. 

Physiology,  ii,  479;  of  bone  mould- 
ing, 285. 

Physoclysti,  104. 

Pickerel,  21. 

Pieris,  230 ;  P.  brassicae,  230 ;  P.  ra- 
pae,  230. 

Pigeon,  21. 


544    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


Pike,  21. 

Pilsbry,  260. 

Pinnotheres  holotkuriae,  242. 

Pipilo  erythrophthalmus,  52. 

Pisces,  87,  95,  98,  192,  195. 

Plagiaulacidae,  324,  345. 

Plagiaulax,  142. 

Plant  variation,  23. 

Plants,  fossil,  77;  evolution  of,  515. 

Platidia,  178,  179. 

Platypus,  135. 

Plectognathi,  106,  107,  108. 

Plectospondyli,  106. 

Plesiosauria,  114,  121. 

Pleuracanthus,  372. 

Pleuronectidae,  238. 

Plicatula,  267. 

Pliny,  227. 

Pliocene,  387. 

Plistocene,  149,  168. 

Podopterygia,  100. 

Poebotheriidae,  302. 

Pollard,  89. 

Polygamy,  390. 

Polymastodon,  142. 

Polymastodontidae,  324. 

Polynesians,  154. 

Polypedates,   68 ;    P.    quadrilineatus 

D.  &  B.,  68. 

Polyprotodontia,  140,  143. 
Poiypterus,  89. 
Polyzoa,  202. 
Porifera,  80,  81. 
Pouchet,  498. 
Poulton,  E.  B.,  230,  237,  381,  392,  393, 

439,  449,  461. 

Pre-Carboniferous  age,  421. 
Pressure,  286,  292,  295,  340,  405,  519. 
Principle  of  improvement,  527. 
Proal  mastication,  318. 
Proboscidia,  128, 132, 133, 136,  141,144, 

297,  305,  306,  309,  318,  321,  329,  330, 

33L  332,  345,  36o,  382,  519. 
Procolophonina,  87.  88. 
Procyonidae,  48. 
Production  of  colors  in  lepidopterous 

pupae,  230. 
Prognathism,  417. 
Proportions  of  limbs  and  of  their  seg 

ments,  305. 
Prorastomus,  330. 


Protective  colors,  392. 
Proteida,  109,  no,  in. 
Proteles.  146. 
Proterotherium,  359. 
Proterotome  mastication,  318. 
Proteus,  242. 
Prothallium,  455. 
Prothippus,  149,  359. 
Protodonta,  388. 
Protophyta,  75,  76,  77,  172. 
Protoplasm,  composition  of,  483. 
Prototheria,  88,  324  360,  374. 
Protozoa,  75,  79,  81,  83,  172,  219,  249, 

252,  505. 
ProtozoOn,  459. 
Psalidodect  mastication,  318. 
Pseudis,  71. 
Pseudosauria,  109. 
Pseudosuchia,  116. 
Psittacotherium,  329,  346,  351. 
Ptenophus  garrulus  Smith,  73. 
Pteridophyta,  77,  79. 
Pterosauria,  115. 
Ptilodus,  324. 

Puerco,  139,  140,  141,  147,  150, 156,  403. 
Putorius  erntineus,  50. 
Pygopodidae,  123. 
Pythonomorpha,  120. 
Pyxicephalus,  71. 

Quadrumana,  132,  133,  136,  143,  293, 

294,  3o6,  326,  332,  360,  361,  467. 
Quebec  group,  413,  420. 
Quenstedt,  189. 
Quiscalus  purpureus,  52. 

Rabl  RQckard,  94. 

Raccoon  pacing,  299. 

Rachitomi,  109,  no,  in,  372. 

Radiant  energy,  484. 

Rana  agilis  Thomas,  68  ;  R.  catesbey- 

ana,  68 ;    R.  chrysoprasina,  68  ;  R. 

clamata,  68 ;  R.  hexadactyla,  68  ;  R. 

temporaries,  64. 
Ranidae,  65,  70,  71,  389. 
Raphanus  raphanistrum  L.,  227;  R. 

sativus  L.,  227. 
Recapitulation,  453,  492. 
Reduction  of  digits,  309. 
Regeneration,  455. 
Reptiles,  degeneracy  of  the  eye  of 


INDEX. 


545 


219;  degeneracy  of  the  limbs  of, 
218;  degeneracy  in  the  skeletal 
structure  of,  122 ;  development  of 
the  brain  of,  122  ;  line  of,  113  ;  suc- 
cessive changes  in  the  structure  of 
the  skull  of,  1 16;  vertebral  articu- 
lation of,  121. 
Reptilia,  88,  94,  95,  98,  no,  114,  116, 

120,  122,  132,  172,    193,    195,    209,    2l8, 

289,  303,  304,  363,  365,  366,  374,  388. 
Retardation,  9,  201. 
Retrogressive  evolution  in  the  Verte- 

brata,  145. 
Reyher,  277. 
Rhinoceros,  313.  314. 
Rhinocerus  unicorm's,  300. 
Rhipidopterygia,  91,  100,  101,  172,  366. 
Rhizopoda,  249. 
Rhynchocephalia,  114,  116. 
Rhynchocyonidae,  305. 
Rhytina,  331. 
Riley,  C.  V.,  531. 
Rodentia,  135,  519. 
Romanes,  vi,  471. 
Rose,  333- 

Roux,  W.,  283,  284.    * 
Rusa,  196. 
Ryder,  J.  A.,  79,  309,  3",  3*9,  320,  321, 

323,  346,  349,  366,  404,  455,  485,  486, 

518,  519,  520,  521,  529,  530,  531,  532. 

Salamandra,  199. 

Salientia,  109,  no,  172,  196,  197. 

Sandberger,  188. 

San  Diego,  244. 

Sarcothraustes,  335. 

Saturnia,  466. 

Saturniidae,  203. 

Sauermann,  Dr.,  239,  240. 

Sauropterygia,  115,  116. 

Sauvage,  Dr.,  372. 

Scaphiopidae,  65. 

Scaphiopus  holbrookii,  68. 

Scaridae,  108. 

Schisniadernta  carens  Smith,  68. 

Schizocrania,  177. 

Schmankewitsch,  V.,  230. 

Schools  of  evolutionary  doctrine,  13. 

Schuchert,  191. 

Scincidae,  123. 

Sciuridae,  351. 


Scombridae,  108. 

Scott,  W.  B.,  222,  334,  526,  531,  532. 

Scudder,  S.,  465. 

Scyphophori,  106. 

Scytopis,  198,  199. 

Sectorial  teeth,  139. 

Sedgwick,  492. 

Seeley,  88,  120,  123. 

Segmentation  of  the  external  skele- 
ton of  the  Arthropoda,  269  ;  origin 
of,  368. 

Segmentation  of  the  vertebral  col- 
umn, 368;  origin  of,  368. 

Selenodont  dentition,  320;  origin  of, 
323. 

Self-consciousness,  495. 

Semper,  228,  242,  527. 

Sense  perception,  495. 

Sensation,  495,  513. 

Serranidae,  108. 

Sex,  516. 

Sexual  selection,  389. 

Sharp,  B.,  269,  531. 

Shetland  pony,  423. 

Shipka,  161,  163. 

Shoulder  girdles  of  Anura,  64. 

Sigaretus,  261. 

Siluric,  77,  83,  183,  185,  186,  187,  413, 
414. 

Siluridae,  103. 

Simla,  159,  170. 

Simiidae,  157,  158. 

Siphocyprcea  problematica,  260. 

Siredon  lichenoides,  200 ;  5.  mexica- 
num,  59. 

Sirenia,  127,  142,  143,  145.  329,  33O,  352, 
360. 

Skull,  of  man  of  Spy,  161 ;  of  Neander- 
thal man,  162. 

Smilodon  neog&us,  344. 

Solenhofen  slates,  123. 

Sonoran,  29. 

South  America,  50,  154. 

Sloths,  305. 

Spain,  437. 

Spea  hammondii  interment  ana,  68. 

Spencer,  H.,  5,  6,  7,  175,  367,  385,  466, 
476,  517,  5i8,  527- 

Sphenodon,  121. 

Spinous  plants,  228. 

Spondylus,  267. 


546    PRIMARY  FACTORS  OF  ORGANIC  EVOLUTION. 


Sponges,  80. 

Sports,  influence  of,  24 

Spy,  159,  161,  163,  164,  165,  166,  169, 
170. 

Squainata,  114,  115,  116. 

Squillidae,  273. 

Stahl,  EM  501. 

Starch,  481. 

Statogenesis,  485,  496. 

Stegocephali,  88,  109,  172. 

Stegophilus,  103. 

Stentor,  250. 

Stereognathus,  325. 

Stevenson,  C.,  432. 

Strain,  305,  311,  313,  319,  326,  327,  349, 
281,  485,  519,  521. 

Strepsiptera,  213. 

Streptostylica,  114. 

Sturnella  tnagna,  52. 

Stypolophus,  335. 

Stypolophus  ivhitite,  339. 

Successional  relation,  19,  62. 

Suidae,  69. 

Suoldea,  318,  324. 

Sus,  330. 

Symphysis  mandibuli  of  a,  chimpan- 
zee, 164;  gorilla,  164;  liegois,  166; 
orang,  164;  Parisian,  166;  Spy  man, 
164  ;  Spy  woman,  164. 

Synagodus,  59. 

Synapta  digitata,  213. 

Systems  of  evolution,  13. 


Table  of  the  characters  of  the  mam- 
malian skeleton,  139. 

Tachyglossus,  135. 

Ta3ker,  195. 

Tahitian,  168. 

Tapir,  313. 

Tapiridae,  318. 

Tarsipes,  146. 

Tarsius,  155,  306. 

Taxeopoda,  128,  136, 146,  297,  357;  car- 
pus of, 

Taxidea  americana,  50. 

Teeth,  evolution  of,  318,  522. 

Teidae,  123. 

Teleology,  20. 

Teleostomata,  91,  99,  100,  101,  336. 

Tellkampf,  Dr.,  241. 


Terebratellidae,  178,  179,  180. 

Termites,  500. 

Tertiary,  184,  291,  421. 

Testudinata,  114,  115,  116,  119,  133. 

Texas,  50,  436. 

Theory  of  internal  causes,  527. 

Theory  of  use  and  disuse,  3. 

Theriodonta,  115,  116. 

Thermochemistry,  483. 

Theromora,  88,  114,  115,  116,  120,  i2i; 

132. 

Thoatherium,  359. 
Thoraceras,  186. 
Thoropa  miliaris  Sphix,  68. 
Thylacinus  cynocephalus,  22. 
Tillodonta,  140,  143,  145,  329,  360. 
Tomes,  381. 

Tontitherium  rostratum  Cope,  156. 
Topinard,  P.,  153,  155,  157,  168,  165. 
Tornier,  E.,  283,  284,  528. 
Tortoises,  114. 
Tortricidae,  123. 

Toxodontia,  128,  143,  297.  330,  360,  382. 
Trachycephalus,  198. 
Trachypteridae,  108. 
Trachystomata,  109,  in. 
Tragulidae,  69. 
Traquair,  99. 

Trias,  108,  113,  135,  184,  209,  325,  417 
Triboloceras,  186. 
Trichea  van'a,  220. 
Triconodon  Owen,  343. 
Triconodontidae,  318. 
Trichophanes,  104. 
Tridacna,  265. 
Trilobita,  83. 
Trimen,  R.,  231. 
Trinil,  man  of,  159,  168,  169,  170. 
Trionychidae,  303. 
Tripteroceras,  186. 
Tristichopteridae,  91. 
Trityloden,  325. 
Trivia,  260. 
Trotting  horses,  426. 
Troglocaris,  242. 

Tubularia  mesentbryantheniuntt  456, 
Tunicata,  172,  214,  218,  362. 
Turbot,  499. 
Tyndall,  Prof.,  476. 
Typhlogeophis,  123. 
Typhlogobius,  244. 


INDEX. 


547 


Unconsciousness,  494,  507. 

Uinta,  147. 

Uintatherium,  354. 

Uintatheriidae,  318. 

Uma,  73. 

Unguiculata,  140,  143,  374. 

Ungulata,  138,  140,  142,  143,  147,  205, 

248,  295,  297,  302,  321,  330,  340,  353. 

355,  357,  36i,  374,  39° ;  origin  of,  209. 
Unionidae,  203. 
United  States,  49,  53,  315. 
Urochorda,  82. 
Urodela,  109,  no,  172. 
Uropeltidae,  123. 
Uroplates,  88. 

Ursus  arctos,  21,  22 ;  U.  maritintus,  21. 
Unspecialized,  doctrine  of,  173. 
Use  and  disuse,  doctrine  of,  9. 

Vandellia,  103. 

Vanessa  to,  232 ;  V.  urticae,  232. 

Variation,  21. 

Variation,  of  basal  lobes  of  leaves, 
5;  causes  of,  225;  in  cicindela,  25; 
cnemidophorus,  41 ;  embryogenic, 
444 ;  fortuitous,  444 ;  gamogenic, 
444;  geographical,  47;  gonagenic, 
444  ;  in  North  American  birds  and 
mammals,  45  ;  origin  of,  225,  497  ; 
ontogenetic,  444  ;  in  Osceola  doliata, 
29 ;  phylogenetic,  444. 

Variations,  of  specific  characters,  25  ; 
somatogenic,  444  ;  structural  char- 
acter, 58. 

Varigny,  229. 

Vermes,  80,  81,  82,  83,  172,  263,  268, 
368,  437. 

Vertebral  centra,  forms  of,  308. 

Vertebrata,  brain  and  nervous  sys- 
tem of,  94,  139 ;  classification  of, 


93;  circulating  system  of,  93,  192; 

origin  of,  81 ;  phylogeny  of,  81. 
Vestinautilus,  186. 
Vilmorin,  228. 

Virchow,  Prof.,  159.  169,  467. 
Vise,  416. 
Vola,  266. 
Volutidae,  260. 
Volutimorpha,  260. 
Volvox,  79. 
Vom  Rath,  470,  471. 
Von  Baer,  175. 
Von  Brunn,  403. 
Vulpes  alopex,  48 ;   V.  cinereoargenta- 

tus,  48  ;   V.  lagopus,  48  ;   V.  velox,  48. 

Wallace,  A.  R.,  3,  5,  228,  381,  383,  387, 

391,  392,  466. 
Ward,  L.,  531. 
Wasatch,  139,  146. 
Weale,  M.,  231. 
Weismann,  10,  u,  12,  23,  203,  399,  424 

438,  450,  458,  459,  480. 
West  Indies,  387. 
White  River,  139. 
Wiedersheim,  366. 
Wilson,  E.  B.,  457,  487. 
Wood,  T.  W.,  230,  231,  233,  234. 
Woodward,  A.  S.,  372. 
Wortman,  293,  402,  520. 
Wundt,  498. 
Wurtenburger,  189.  191. 

Yucatan,  49. 

Zeller,  242,  243. 
Zencedura  macrura,  58. 
Zeuglodon,  304. 
Zittel,  Dr.,  370. 
Zittelloceras,  186. 
Zygophyta,  77. 


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